Brown Spots on the Leaves of Green Beans

runner bean plant 6 image by chrisharvey from Fotolia.com

Green beans are a dependable producer for either the large farm or the backyard vegetable garden. Also called snap beans, this popular garden bean includes both bush and pole varieties. Even though this prolific plant is easy to grow, bean plants can be susceptible to a variety of diseases.

Alternaria Leaf Spot

Alternaria leaf spot causes circular, dark-brown blotches that eventually turn gray and fall out leaving behind holes with dark rings on the leaves. The disease can occur at any time during the season and is prevalent on plants that have been injured by spider mites or are showing signs of stress due to a lack of nutrients. Prevention includes controlling problem insects and maintaining sufficient soil nutrient levels. The University of Minnesota Extension notes that “(n)o fungicide is currently registered for control of this disease.”

Anthracnose

According to the University of Florida Extension, the fungus, anthracnose, “causes yellowish-brown or purple-colored, irregular, sunken spots with dark reddish-brown borders.” These spots later turn to dark brown. Spores are spread by water. Prevent infection by planting resistant varieties, avoiding overhead watering and handling plants while wet, destroying infected plants, rotating crops and spraying regularly with a safe fungicide.

Bacterial Blight

Bacterial blight is a disease that begins as large brown patches on the leaves and eventually kills the plant. Effective control includes planting certified blight-free seeds, avoiding handling plants while wet and spraying with products containing Bacillus subtilis, a bio-pesticide.

Mosaic

Mosaic is a virus. The leaves of infected plants become mottled with light green and yellow area and can be deformed. Plant growth is stunted. Mosaic is spread through aphids, cucumber beetles, whiteflies and infected seeds and lives in many varieties of weeds. Prevent mosaic by planting disease-free seeds of resistant varieties and controlling virus-bearing weeds and insects.

Rust

Rust is a fungus that forms powdery, cinnamon-brown spots on leaves and pods. An unchecked rust infection will greatly reduce yield and eventually kill the crop. Rust fungus spores are spread with the wind and thrive in moist conditions. Disease management includes planting resistant varieties, regular spraying of fungicides, rotating crops and avoiding overhead watering.

My Beans Have Brown Spots

Bean Spots Have Multiple Causes

Insects, disease and age can all result in brown spots on beans, as can water problems (which may encourage disease). They include:

  • Anthracnose – fungus; severe damage near soil line.
  • Bacterial Brown Spot – water-soaked spots on foliage are brown with yellow margins.
  • Bacterial Blight – spots on both leaves and pods; rust-colored and may ooze yellow fluid.
  • Insects – aphids, various beetles and whiteflies cause chewing damage.

Brown Spots on Harvested Beans

With green beans (any bean harvested in the immature stage), the most likely reason for brown spots is that the beans are past their prime. They aren’t unsafe to eat, but you might want to use them in soups, stews or casseroles rather than as a stand-alone side dish. Store them in a plastic bag in the crisper drawer to keep fresh for about a week.

Brown Spots From Insects

Insects can cause brown spots in bean pods and bean leaves by feeding on them. In most cases, you’ll see a round hole that’s brown around the edges. Some insects may cause a brown blister-like lump on the bean pod. Although healthy plants can withstand a little insect damage, many insects either spread disease or allow organisms to enter through the holes they chew.

Brown Spots From Diseases

A number of diseases can cause brown areas on beans and bean leaves. Unlike insect damage, these are more likely to appear as irregular splotches, spots or streaks. Bacterial and fungal diseases are the most common culprits. The location of the discolored areas can be a clue to the cause, so inspect plants carefully. Color variations – yellowish, orange or purplish – can also provide clues.

Preventing Brown Spots

Prevention starts with identifying the problem. Check the soil to make sure it is neither too wet nor too dry. It should be moist about one inch below the surface. Look for insects – both flying and crawling – as well as egg clusters. Ensure your soil is fertile to give beans enough nutrition to withstand minor insect attacks. Remove and burn any plant that looks diseased.

Treating Bean Spots

Treatment, of course, depends on the cause. Fungal diseases often result from over-watering or sprinkling the leaves. Use drip irrigation and don’t work with wet plants. Fungal infections often respond to neem oil or tea tree oil, both of which have fungicidal properties. Spray plants every 10 days. Hand pick insects or use approved organic insecticides.

By Robert Harveson, Extension Plant Pathologist

Pathogen

Pseudomonas syringae pv. syringae. The bacterium is a gram negative rod, strictly aerobic with a polar tuft of flagella. It also produces diffusible fluorescent pigments, particularly on iron-deficient media. On standard media, it produces white-cream colored growth. Pathogenic isolates produce a bacteriocin in the host plant known as syringomycin W-1. The host range is very large, including Phaseolus vulgaris, P. lunatus, Lablab niger , Glycine max,Pueraria hirsute, Vicia faba, Vigna sesquipedalis, and V. sinensis.

Disease Symptoms

Lesion size can vary, but generally are small, circular, and brown, coalescing to form linear necrotic streaks delimited by leaf veins and veinlets. If water soaking occurs, it manifests itself as small circular spots on the underside of leaves. The centers of old lesions fall out leaving tattered strips or “shot holes” on affected leaves and evidence of water soaking may be visible in the edge of tissue next to the shot holes (16,28). Stem and petiole lesions are occasionally found in situations where the pathogen becomes systemic. Lesions on podsare circular and water-soaked initially, but later turn brown and become necrotic. If young pods or those in the flat stage become infected, they may be bent or twisted with visual ring-spots or water-soaked, brown lesions.

Coalescing to Form Linear Necrotic Streaks Water Soaking (H. Schwartz)
Lesions on Pods (H. Schwartz)

Favoring Environmental Conditions

Like the other dry bean bacterial pathogens, the brown spot pathogen survives in residue or seeds from the previous year. It is very similar to the halo blight pathogen (P. syringae pv. phaseolica) by producing fluorescent pigments. It differs from the halo blight pathogen by being favored by warm temperatures (80-85 F) as opposed to the cool weather favoring disease development of halo blight (68-72 F). Wet weather, hail, violent rain and windstorms help the pathogen to spread among and between fields. Continuous bean cropping also helps the pathogen survive in infected debris.

Management

Genetic Resistance

Use seed that is certified to be disease-free.Several pinto cultivars are available with tolerance, such as Chase and Poncho.

Cultural Practices

In general, practices that limit disease losses to other bacterial pathogens will also be effective with brown spot. Don’t spread old bean straw into fields to be planted with beans. Avoid going into fields that are wet. Other cultural practices for management include avoiding the reuse of irrigation water, and incorporating infected debris after harvest and rotating out of beans with other crops for at least two years, and managing volunteer beans.

Volunteer Beans

Chemical/Biological Control

Treating seed with streptomycin helps to reduce contamination of the seed coat. Using of copper-based sprays at the mid vegetative to flowering stages will also help to provide some control.

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Bush bean leaves turning brown

Do all ripout first, then while you have everything open, start putting it back. I had a whole house that I’m still living in, damage driven. I ripped floors to the joists then replaced them, and since I needed to tackle wiring, water, windows and ‘liveability’ as well as some retros for more energy efficient…. Identify all structural walls before you touch anything. Identify all circuits; what is on what, and label them clearly. (I put masking tape on wall at each outlet or fixture and used a trouble light laid where I could see it plugged into the outlet I was checking on the panel… and check BOTH outlet sockets. I have run into something wired separately! Then went through and tagged all lights and light switches. Get one of those circuit tester things that light up, and be religious about using it. Identify all water; all shutoffs, what they shut off, if they will shut off; and if it doesn’t have a shutoff, where can you turn it off, even if it means turning off at the meter. If it involves Natural Gas, don’t touch it and call a pro. That one is not negotiable. I had a leak under at my furnace a couple of years ago, and the city’s sniffer unit was literally lost (it may have walked and they had to buy a new one) and the gas company’s was broken at the repair; so we ended up buying our own. I can test for leaks but I let the pros do it. Beware of needing permits and pull them!!!!!!!!!! Some things may not be up to code, but are grandfathered in. Once you touch it, you have to bring it up to code. In older construction you might run into asbestos, especially for pipe insulation. It is manageable, sometimes it is ‘encased in place’ and left, sometimes it has to be abated. Big thing is don’t let it get airborne. If you find black mold you will have to encase in place, abate (remove) and probably replace what wood has been affected. I have done the latter myself, it is a PAIN but possible to do correctly and safely. One you have done ripout and tracing, schedule replacement… I did have gas furnace, main power, and gas water heater moved, and the connections for the gas stove moved. In order: permits. Ripout. Assess anything hidden. Contain/repair/replace any hidden damage first. This can be leaks in ceiling, mold in walls, crumbling structural… Repair outside shell first if needed, you need to stay weathertight. If you are going to replace windows, siding, roof; do those first. If you have to redo insulation, do it after that tempered by having to run wiring or plumbing. Moving to inside shell; if anything needs code compliance, do that next. I did water first, then gas, then electrical. I had a 100 amp feed, code is now 125, and I went to 200, and changed circuits (added some, and replaced wiring and outlets on some existing to bring them from 15 to 20 amp) Then start closing up, floor first so you can walk safely; and I laid all my floors. THEN covered and protected my floors with luan, cardboard, drop cloths… At the time you touch the electrical… I had the pole to mast replaced (gratis, power company) and electrician to do meter to new box and the box was moved. I did most of the grunt work and everything was open to be inspected, saving me a lot of $ on having the electrician in. Take pictures of any open wall or floor, this is your Xray eyes later. Borrow a good high resolution high megapixel camera to take these, you want all the detail you can get. Furnace move was a minimal of gas and electricity and I was able to do my own duct work after for the changes. Plumbing I did almost all of it, worst part was learning how to work with PEX. I had plumber in mostly to help some of the wastewater piping and getting the toilets, tub, and showerpan seals right to the wastewater and my venting correct. No sewer gas and no LEAKING. Then move to drywall and fixing walls, reskinning that and/or ceilings. THEN, sinks, toilets, shower pans and tubs. You may have to juggle on when you have your plumber in, on repairing floor/laying floor; and reskinning the wall, whatever they need to install at the time. As in stand by and be ready. Some things are better if the walls and floors are open, some stuff may be needed to be done after. You might have to have the plumber come twice to be more economical in your overall progression. Kitchen cabinets need to be in to have countertops done, which have to be done before the sink can be finish installed and the faucets and disposer; and dishwasher. If you are having an electrican come in to do work, they may have to come to hook up appliances in the kitchen and/or laundry room. A possible 2 visits by the electrician as well. Laundry room is on the same time schedule as your kitchen…. usually though you can have that all finished up and ready for the W/D to be put in place. If you are DIYing, your walls get paint and the last of the fixtures go on (outlet covers, attaching wall sconces and ceiling mounted pendant lights) in that order. Kitchen and bathrooms then get their tile/backsplashes. I did floor tiling in bathrooms at time of floor reinstall and put most of my plumbing in place at that time; plumber did most of the waste work one day then came back a couple days later to put the connections for toilet and showerpan and tub; and stubbed and capped the three sinks and the washer drain. The kitchen and bathroom finish tiling (aka countertops and backsplash) will be amongst the last work I do. Hope you get an idea on the sequencing; about the only thing I didn’t have to do was completely reside, and reroof. I do have a small hole to deal with where I removed a corner fireplace that was more of a hazard than it was worth… through my roof, I tore it out Sunday. Then I will be shell tight again… Plan at least 20% for overruns. When you buy supplies like drywall, dimensional lumber, plywood, buy 10-15% more. Get the extra pail of thinset if you are playing with tile, it will take more than you can imagine. If you get hit with a structural issue, all bets are off on budget. (that is what happened to me). If you are buying flooring, tile, brickwork, veneer stone, pavers, buy 20% more as you may have one odd lot and have to open everything and mix it in; or work with the one off tint lot as a ‘design feature’. If you have more than one container of paint (can or pail) get a large enough container to open ALL of the batch into and mix it, you may have one offtint (I’ve seen this on house painting) and this will make it all the same. If you are your own general contractor, you are THE person to run if a sub is out of something or needs something. Their time costs you money and you have to keep them going. If something goes sideways you have to fix it or find it. If there’s something that has to be done to keep it on schedule and you elect to do it yourself you HAVE TO DO IT on schedule and on time. (doing your own demo) Renting a skip dumpster, some places need a permit just to park it at the site; and there are many that either want to dump something INTO your dumpster or ‘raid it’ for what’s in it. Be warned. And there are some things you can’t put in a dumpster. Also beware of the load limits and level of debris.

My bean leaves are developing yellow patches and are either browning and falling off or just falling off. Is this a disease, deficiency, or something else?

A nitrogen deficiency causes leaves and plants to be light green or yellow. The vine may also suffer from slow, inadequate growth and produce few flowers. A manganese deficiency causes older leaves to turn yellow and develop dead brown spots.
Root-knot nematodes, microscopic parasitic worms, infest the roots of the beans and prevent them from absorbing nutrients. The leaves yellow and the plant’s growth is stunted. Soil solarization when the soil is cleared kills nematodes.
Mosaic disease affects beans by producing mottled yellow patches on leaves and yellowing of plants. Planting mosaic-resistant varieties is the only solution for the virus. Bacterial blight causes spreading yellow spots on leaves. Keeping leaves dry can help prevent fungal diseases. Bean rust symptoms include yellow leaves with brown dust on the undersides. Rust infects plants in cooler weather. Multiple applications of sulfur spray can control the fungus and should begin when rust first appears.

Broad bean, dry

Description

Broad bean, Vicia faba, is a leguminous plant in the family Fabaceae primarily grown for its edible beans. Broad bean is a an annual vetch reaching between 0.5–1.8 m (1.6–6 ft) tall. There are often multiple stems originating from the base of the plant and the compound leaves are often broad, oval shaped, and come groups of 6 leaflets to a stem. The flowers are white with purple markings. Between 1 and 4 pods develop from each flower cluster. The beans can be greenish black, brown or black in color. Vicia faba may also be referred to as bell-bean, fava bean or horsebean and originates from the Mediterranean or in South-West Asia.
Broad bean plant in flower
Broad bean pods
Broad bean foliage
Purple broad bean variety
Broad bean pods ‹ ×

Uses

Broad bean is cultivated for both animal and human consumption, soil development, and medicinal uses . It can be served fresh, dried, canned, or as a substitute for meat and skim-milk. Broad bean is often used as either forage (leaves, plant material) or silage (fermented, high-moisture fodder) for animals. Using broad bean as a spring cover crop allows for protection against erosion, and can be tilled back into the soil as green manure. The taproot also has the added benefit of being able to break-up hard compacted soil.

Propagation

Basic requirements Broad bean is a cool-season crop and should be grown in early Spring or late summer to avoid high summer temperatures. Broad beans will grow best at soil temperatures between 15.5 and 18.3°C (60–65°F) and will not grow well at temperature below below 4.4°C (40°F) or above 23.8°C (75°F). Broad bean is particularly susceptible to high temperatures during the summer which make the plants unproductive. Broad beans will grow best in a fertile, well-draining soil with a pH between 6.0 and 6.75 positioned in full sunlight. Sowing seeds Broad beans should be direct seeded in the garden in Spring as soon as the soil is workable and temperature is above 4.4°C (40°F) with the optimum temperature for germination being between 10 and 21°C (50–70°F). A second planting can be made in early Fall in areas with moderate winters. Seeds should be planted 2.5–5.0 (1–2 in) deep allowing 7.5–15 cm (3–6 in between plants and approximately 0.6 m ( 2 ft) between rows. General care and maintenance Broad bean plants are bush-like but can grow quite tall and will benefit from staking to provide some support and keep them from flopping over due to the weight of the pods. Keep soil moist during flowering to ensure optimum pod development and soak ground thoroughly if plants come into flower during a dry spell. As they are legumes, broad beans generally do not require additional fertilization as long as they have sufficient root nodules. Nodulation can be promoted by inoculating seeds with additional Rhizobacteria prior to planting. Harvesting Broad beans are ready to harvest when the pods are fat and full and beginning to droop from the plant due to the weight of the seeds inside. Seeds can be dried either by leaving pods on the plant until they begin to shrivel or by picking and hanging up to dry out.

Broad beans will benefit from staking to support the weight of the pods ‹ ×
CABI Crop Protection Compendium. (2013). Vicia faba datasheet. Available at: http://www.cabi.org/cpc/datasheet/56364. . Paid subscription required. Duke, J. A. (1983). Vicia faba L.. Purdue University Center for New Crops and Plant Products. Available at: http://www.hort.purdue.edu/newcrop/default.html. . Free to access. Schwartz, H. F., Steadman, J. R., Hall, R. & Forster, R. L. (2005) Compendium of Bean Diseases. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/43275.aspx. Available for purchase from APS Press. Sattell, R., Dick, R. & McGrath, D. (1998). Fava Bean (Vicia faba L.). Oregon State University. Available at: http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/15226/em8697.pdf. . Free to access.

Broad Beans

Broad beans offer one of spring’s best seasonal flavours.

And as well as tasting good they enrich the soil with nitrogen, and handle the toughest frosts so can be planted now in all areas of Australia.

Linda has the low-down.

Photo – photolibrary.com

Broad beans grow like crazy through winter and their beautiful white and black, pea-shaped flowers appear in winter and early spring. They do stretch your patience though as it seems an age before the beans themselves appear, and then when they do come, the harvest is quick, and the kitchen preparation quite lengthy! Broad beans are much larger than the usual warm season green beans, and they need to be shelled. I like the young beans simply shelled and steamed. Restaurant chefs always double pod them, popping them out of their pale green inner shell after blanching to reveal the bright green bean beneath. By the end of the season the pods are quite large, the flavour stronger and the beans are often pureed.

Position

Ideally, choose an open, sunny position for planting. Because of the pretty flowers I have seen them used as a loose kind of hedge all the way along a front fence. These are very hardy, frost-tolerant vegetables.

Photo – nito/.com

Soil Preparation

Prepare soil well ahead of planting by adding compost or manure. Horse, cow or sheep manure is helpful as these manures have low nitrogen content. Broad beans make their own nitrogen so its best to avoid using fertilisers that are high in nitrogen, such as chook manure and fish emulsion. Spread cow manure over your bed 5cm thick and dig in well. Add sulphate of potash at the rate of one tablespoon every square metre and water in well. For acid soils, add a dressing of lime or dolomite – one handful per square metre – to sweeten up the soil and provide the best conditions for broad beans.

Growing guide

From March to May, sow broad beans directly into the soil. Plant 2 beans together 10cm apart down your rows. Rows should be 20cm apart. Water once and don’t water again until you see two open leaves. Over-watering is the biggest cause of germination failure.

Growth

While young, broad beans are self-supporting, but as they get taller they will get very top-heavy with pods. Planting in double rows is helpful as the plants can lean on each other, but I like to place stakes at the corners of the garden bed and tie strong string around the stakes, which helps hold up the beans.

Pests and diseases

Broad beans are very easy crops to grow and are largely untroubled by pests and diseases. Simply allow enough room between plants so that good airflow can inhibit fungal diseases.

Photo – azure/.com

Tips & Tricks

Buy your beans seeds from any good seed-growing outlet. I like Fothergills, Greenpatch Organic Seeds and Eden Seeds.

Harvest constantly to ensure a continuous crop.

Old, late season beans need to be double-shelled. First peel, then blanch the pale green beans, drain and when cool enough to handle, pinch the end to slip the tender bright green bean out of its skin.

Shelled broad beans freeze well. Blanch in a rolling boil for 2 minutes, cool with icy water for 2 minutes, drain and freeze in freezer zip lock bags for use later. This ensures your family doesn’t have to eat broad beans daily for four weeks!

Rotate crops each year so broad beans enrich soils and add nitrogen into all parts of the vegie patch.

Broad Bean varieties

Coles Dwarf Prolific produces heavy crops on 1m-high plants.

Crimson Flowered has red flowers instead of black/white and good tasting beans. Grows to 90cm.

Early Longpod to 1.5m produces large pods.

Aquadulce is a dwarf heirloom variety usueful for windy areas. Pods get to 20cm long.

Text: Linda Ross

This guide is provided to help growers and agronomists identify common faba bean diseases in the field including ascochyta blight, cercospora leaf spot, chocolate spot, alternaria leaf spot and rust. Correct identification is important because different fungicides are used to manage different fungal diseases.

In particular ascochyta blight, chocolate spot and cercospora leaf spot, which all infect leaves of faba beans, may be confused with each other. These three diseases can be distinguished by the following features:

  • Lesions of ascochyta blight contain pycnidia (black dots) in the centre (Figure 1) whereas no pycnidia develop in lesions of cercospora leaf spot or chocolate spot.
  • Leaf lesions of ascochyta blight may drop out the centre leaving a hole in the leaf.
  • Cercospora leaf spot and ascochyta blight first appear during winter, whereas chocolate spot first appears in late winter or in spring.
  • Ascochyta blight on stems often appears during winter as sunken lesions with visible pycnidia, whereas cercocspora leaf spot on stems appears later as flatter lesions with superficial penetration of the stem wall.
  • Chocolate spot initially develops as a scatter of small brown spots on leaves (Figure 3A), of which many eventually expand into lesions and rapidly coalesce, whereas cercospora leaf spot and ascochyta blight commence as distinct lesions on leaves that coalesce slowly.
  • Chocolate spot develops lesions (spots) on flowers but neither cercospora leaf spot nor ascochyta blight infect flowers.
  • Cercospora leaf spot lesions are typically exhibited on leaves on the lower 50% of the plant during winter, with stem lesions appearing after this time, whereas ascochyta and chocolate spot symptoms can appear on any parts of foliage in the canopy.
  • Cercospora leaf spot causes defoliation of the lower canopy, from late winter, whereas this is not typical in plants affected by the other fungal diseases.

Ascochyta blight

Symptoms

Ascochyta blight is caused by the Ascochyta fabae fungus. Initially, look for pale grey lesions with dark margins which change to dark brown/grey lesions, depending on leaf wetness, showing through on both sides of the leaves. As the spots enlarge, they develop grey centres which may contain black dots (pycnidia). The centre of the spots may fall out to produce a ‘shot hole’ appearance when conditions become dry (Figure 1). ‘Running’ lesions down affected leaves are typical during wet conditions.

Figure 1 Black dots (pycnidia) visible within infected lesions. Source: Frank Henry, Agriculture Victoria and Rohan Kimber, SARDI

Lifecycle

Ascochyta fabae spore germination occurs between 15 and 25°C, with an optimum of 20°C, at high relative humidity. Spores are mostly spread to adjacent leaves by rain splash. After landing on a susceptible leaf, the spore will germinate and initiate a new infection if the leaf surface remains wet for 12 to 24 hours. Ascochyta survives and spreads from seed and previously infected stubbles.

Growing a resistant variety is the first step to manage ascochyta blight. However, a ‘new’ A. fabae strain (pathotype 2) was found in South Australia and isolated areas of Victoria during the 2015 growing season. This strain (pathotype 2) is now widespread across both Victoria and South Australia. The new strain of ascochyta blight has overcome the resistance in Farah, making it equally as susceptible as Fiesta. It has also partially compromised PBA Rana, PBA Zahra and PBA Marne, with both requiring some fungicide applications during podding to prevent seed staining. PBA Samira, Nura and PBA Bendoc remain resistant to both strains of the pathogen.

Susceptible and moderately susceptible cultivars should be sprayed with an appropriate fungicide 5-8 weeks after sowing and further sprays may be required ahead of rain fronts, particularly during podding to prevent pod infection, seed abortion and seed staining.

See the Victorian Pulse Disease Guide for more information on resistance ratings for ascochyta.

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Cercospora leaf spot

Cercospora leaf spot (CLS) is a fungal disease caused by Cercospora zonata. The disease leads to the development of red-brown to dark-grey leaf spots or lesions which are irregular and tend to be darker and more angular in shape compared to chocolate spot lesions. A concentric ring pattern can often be seen within lesions. Older lesions develop a slightly raised, deep red margin (Figure 2). The disease mainly affects leaves, but it can also infect stems and pods.

Figure 2 A) Cercospora may develop slightly raised red margin and concentric ring patterns B) Cercospora is generally darker in colour compared to chocolate spot, however they can occur together on the same plant. Source: Frank Henry, Agriculture Victoria and Rohan Kimber, SARDI

Long periods of leaf wetness and low temperatures (7 to 15°C) can allow early establishment of CLS. Moderate disease severity occurs between 9-17°C with 72h leaf wetness. Rapid expansion of lesions occurs when temperatures rise from 20-25°C. Cercospora has an 11 day latent period. Defoliation of the lower canopy results from severe cercospora leaf spot.

CLS originates from soil-borne inoculum and previously infected plant material and is spread during the season by conidia that dislodge from short white spore clumps on the surface of lesions.

All the current varieties of faba bean are susceptible to the cercospora fungus and an application of a suitable fungicide, 5-8 weeks after emergence, is necessary for the control of cercospora leaf spot. This is especially important in regions with a long history of faba bean cropping and paddocks with close rotations of faba beans.

See Pulse Australia for information on critical stages for fungicide control in faba beans and the Faba bean fungicide guide for 2018.

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Chocolate spot

Chocolate spot is mainly caused by Botrytis fabae, but Botrytis cinerea can play a minor role. Symptoms are varied, and range from small red/brown spots on leaves to complete blackening of the entire plant.

Two stages of the disease are recognised. First, the non-aggressive phase, when discrete reddish-brown spots are ‘peppered’ over the leaves and stems. Lesions may have a red-brown border, with a lighter coloured interior. Next an aggressive phase occurs when spots darken in colour and coalesce to form larger grey-brown necrotic lesions, that may eventually affect the entire plant (Figure 3). The fungus is most aggressive in humid weather. Masses of grey spores become visible on dead plant tissue increasing inoculum load, and often visible to the naked eye, protruding from diseased tissue in high humidity and calm conditions. These symptoms are also expressed on flowers. Sometimes, small black sclerotia may be found inside the stems of badly diseased plants.

Figure 3 A) Chocolate spot lesions may have a red brown border, the interior is lighter in colour B) Chocolate spot infection on flowers leads to abscission which can drastically reduce grain yield. Source: Frank Henry, Agriculture Victoria and Rohan Kimber, SARDI

Botrytis (chocolate spot) requires extended periods (>25hrs) of leaf wetness or high humidity (>70%) within the crop canopy and temperatures between 15–28°C for disease development. The optimum temperature is 18-22°C. This typically occurs during flowering and canopy closure. If not controlled, chocolate spot can cause up to 90% yield loss as flowers and growing tips are particularly susceptible, with severe stem and leaf infection also possible. When humidity levels decrease or maximum daily temperature exceeds 28°C, the infection levels decline sharply. The chocolate spot fungus has a very short latent period of 1-3 days.

Botrytis survives on infected debris as mycelium or sclerotia, or directly in the soil as sclerotia. Low levels of seed-borne inoculum have also been reported.

No varieties have resistance to chocolate spot but improvements have been gained, with the latest varieties PBA Samira and PBA Zahra rated as MRMS. Crops should be sprayed with an appropriate fungicide at early flowering or onset of canopy closure, and additional sprays may be required in humid seasons.

See the Victorian Pulse Disease Guide for information on chocolate spot resistance ratings and Pulse Australia for the Faba bean fungicide guide for 2018.

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Alternaria leaf spot

Alternaria leaf spot is caused by the fungal pathogen Alternaria alternata. Dark lesions often have a red-brown margin, with obvious concentric rings or target spots (Figure 4). Lesions do not develop black dots (pycnidia) like ascochyta.

Figure 4 Alternaria dark lesions often have a red-brown margin with concentric rings. Source: Frank Henry, Agriculture Victoria and Rohan Kimber, SARDI

Alternaria is a weak pathogen that is usually considered a secondary pathogen that only attacks following damage by other fungi or insects. Spores are produced on infected plants or crop debris and are spread by wind and rain to other plants, where they remain until conditions turn warm (15°C to 20°C) and humid. Alternaria leaf spot develops in excessively wet seasons. Hot and dry conditions interrupt epidemics as the absence of moisture greatly reduces spore production.

Alternaria can survive on seed, infected crop debris and on other hosts, yet is considered a minor disease with control usually not warranted.

Rust in faba bean

Faba bean rust is caused by the pathogen Uromyces viciae-fabae. Look for numerous small, orange-brown pustules each surrounded by a light yellow halo on the leaves. As the disease develops, severely infected leaves wither and may fall from the plant (Figure 5). On stems, the rust pustules are similar, but often larger, than those on the leaves and rust pustules may also appear on the pods. Severe infection may cause premature defoliation, resulting in reduced seed size. The latent period of faba bean rust is at least 10 days.

Figure 5 A) Leaf with Uredospores B) Leaf with teliospores. Source: Frank Henry, Agriculture Victoria and Rohan Kimber, SARDI

Rust is generally found from mid-Spring on and is favoured by warm temperatures (> 20°C). Infection can occur following six hours of leaf wetness, so the fungus does not require extended wet periods. Following infection, the fungus matures after 10-12 days and forms pustules.

Rust commonly occurs late in the growing season during podding, resulting in premature leaf drop which can reduce seed weight and size. Humid and warm conditions (more than 20°C) promote its spread.

The rust fungus survives on stubble and self-sown volunteer bean plants as teliospores (Figure 5D). Teliospores can infect volunteer bean plants directly without the need for an alternate host and infection of volunteer faba bean plants can be an important factor in the early development of rust epidemics. Rust spores from stubble and volunteers are blown onto new crops by the wind and infect plants. The leaves, stems, and pods can all be infected and in-turn, new spores are formed in rust pustules on infected plants.

Faba bean rust is best managed with resistant varieties and fungicides.

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Look-a-like symptoms

  • Herbicide damage (particularly simazine) can be mistaken for ascochyta blight (Figure 6). However, it does not cause lesions with grey centres and black dots (pycnidia) and is usually confined to the edges of leaves. Spotting on leaves from herbicide sprays is common and can be identified by the uniform spread of the spotting and only occurs on one side of the leaf.

Figure 6 Herbicide spotting on faba bean. Source: Rohan Kimber

  • Red-legged earth mite damage can be mistaken for chocolate spot. Symptoms start as silvery patches which become red-brown. They are similar in colour to chocolate spot but form a large irregularly-shaped area.

More information

  • Agriculture Victoria AgNotes Series
  • Victorian Pulse Diseases Guide
  • Victorian Winter Crop Summary
  • Pulse Australia faba bean fungicide guide for 2018
  • Pulse Australia Integrated Disease Management for critical stages of disease control

Acknowledgements

  • Joshua Fanning, Agriculture Victoria
  • Joop van Leur, NSW Department of Primary Industries

This is a plant with a severe case of fava bean rust, or Uromyces viciae-fabae.

No, the plant is not oxidizing. Rusts are plant diseases that give the impression of rusty spots, but really those are pustules (great word eh?) containing fungal spores. Most of the fungus consists of threads called hypae that are all tangled through the plants, robbing them of nutrients in plant sap. The spores released at the surface are ready to float away and find a new plant to infect. Here are some close up shots of the spore pustules:

I see the disease fairly often in San Francisco gardens. It does probably reduce production somewhat, but it often occurs later in the season, after most of the crop has formed. Here are some ways to lessen your chance that it will occur or reoccur:

–This disease is encouraged by wet leaves, so try to water favas at the ground level, rather than sprinkling them. Of course we can’t prevent rain and misty weather, but the less dampness the better.

–If you see the disease early, with only a bit of damage, you might slow it by removing diseased leave, though of course you don’t want to take too many leaves off of the plant.

–If your plants are ripening beans, you will be reluctant to take them out until you harvest, but as soon as you can do so, take th plants out. Do not compost them. In San Francisco, you can put them into a green bin for Recology to compost, since their compost gets very hot and should kill the spores. When you take your plants out, pick up all the fallen and dried leaf debris you can find as well.

–Don’t save and replant seed that came from infected fava bean plants.

–Copper sprays, which are approved for organic farmers, may offer some control. However, they will be a lot of trouble for a small planting, and will harm the soil if used repeatedly.

–A two to three year rotation might help, but if your garden is open to breezes from nearby plantings, the spores may be reintroduced.

(See also on this blog posts on chocolate spot disease and the black aphid that infests fava beans.)


I never have much luck when it comes to any form of bean growing in my vegetable garden. The fungal diseases such as rust seem to get them every time. So my poor Broad Bean crop has copped the latest rust fungal infection.

What causes fungal rust?

A combination of factors. It can be due to slackness in proper crop rotation, an over heavy feeding of manure (high nitrogen levels) into the soil prior to planting, and planting of plants too close together so that the air flow is restricted.

What should be done to prevent rust?

Ideally, crops that you expect may suffer from rust should be planted where they get good morning sun with good air flow. Water the crop in the morning rather than in the evening. Check your soil’s drainage as overly damp soil can encourage fungal issues.
It is better to feed broad beans potash as it hardens the plant and makes them less susceptible to disease. Try combining with a seaweed solution.
Rust can be difficult to treat as it can go into a dormant stage. Often omitting crops that are susceptible for around 2-3 years to help control the problem.

Spraying?

Yates Fungus Fighter or Leaf Curl Copper Spray are often recommended for fungal infections, however, they are only effective if you catch the very first sign of the fungus.
Chemically treating infected plants is not an effective method to contain the disease.
Using any form of a copper sulfate spray is actually not recommended for food crops as the chemical actually is absorbed by the fruit, so the plant that is sprayed should in fact not be consumed from for up to the next 18 months! Apricot tree owners, be warned.

Removing the diseased plants

If you catch the first signs of rust on your plants, simply remove the infected leaf matter immediately, placing them into a plastic bag and placing it into the general rubbish – never the compost or greens recycling.
When removing all the plants, they must be disposed of in a garbage bag and placed likewise into general rubbish also, to contain the outbreak. Remember to dig out the roots, too.

Can we eat the Broad Beans?

Some will eat their broad beans, some won’t. It’s up to the individual.
If the pods show signs of a fungus, do not consume.
Or if the crop is heavily affected, then it’s time to be brave and pull them out entirely without a harvest.

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