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Common Summer Plant Ailments: Early Signs for Early Detection

IMG_3750Mid-summer, right as gardeners begin getting used to the consistent rhythm of tender summer crop harvests, is also the time when diseases are most likely to strike our favorite brassicas, cucurbits, nightshades, corn, and beans. Heat stress, too much or not enough moisture, the life stages of disease-spreading bugs, the extra exertion from producing fruit… all of that can make for an unhealthy combination ripe for disease.

 

Even the best gardeners and farmers will see signs of stress and disease on some crops every season. It’s just part of growing annual vegetables (as well as other crops). Weeds choose to grow in places that best suit their needs and are thus generally stronger than crops we choose to plant in place that best suit our needs. Many growers consider disease resistance when selecting their crops, but most also consider taste, time to maturity, and size of yield. And so, to get the most desirable harvests from favorite varieties means vigilant health monitoring.

The best first course of treatment is (isn’t it always?) preventative. Many overall good gardening practices help create an unwelcoming environment for viruses, funguses, and pests and a happy growing space for plants. Following a crop rotation plan, amending the soil, choosing safe and healthy seeds, controlling pests, and stewarding land organically go a long way in addressing this. Another important consideration for preventing disease is irrigation systems – take a look here for our recommendations for healthy watering methods.

Lastly, if your land or seeds and seedlings planted in past season have a history of disease, good sanitation is essential. Cleaning all tools (here's how), containers, trellising, and row covers will help prevent the disease from reemerging. Keeping diseased plant material out of your compost and away from your garden is important. Planting seeds collected from healthy plants is key.

At this point in the year, the best weapon against outbreaks gardeners have is early detection. Catching symptoms early may mean the difference between losing one or two plants and losing an entire crops. Scouting for spots, colors and deformities is one of the best tools for early detection.

Below are eight common summer plant ailments to look for, and suggestions for how to proceed if you find symptoms in your garden:

Late Blight most commonly affects tomatoes and potatoes and, true to its name, can show up later in the season – after flowering. The first symptoms to look for are watery, grey-green lesions on the leaves and stems. As the disease develops, these spots will enlarge, multiply, spread, and grow a white, moldy-looking center on the underside of the lesions.

Prevent by removing volunteer tomatoes and potatoes from the garden, improving air circulation via pruning and staking, watering only in the morning and avoiding overhead watering, and avoiding handling plants when wet.

Learn more: to help with diagnosing and treatment, take a look at Erin’s article on Troubleshooting in the Tomato Patch (with links to Cornell diagnostic documents).

Bacterial Leaf Spot starts out with small, watery, dark green spots on leaves and attacks Brassica crops and Nightshades. At a later stage, the spots dry out, leaving holes on the leaves and the fruits develop spots (or cracks) too.

Prevent by improving air circulation via pruning or staking, weeding frequently and thoroughly, watering only in the morning, and avoiding handling plants when wet.

Learn more: to help with diagnosing and treatment, take a look at this helpful resource from Cornell University.

Club Root is a fungus that can affect all members of the Brassica family. First signs to look for are wilting, yellowing of leaves, and slow, if any, growth. At a later stage of the infection, the roots of the plant will form ping-pong sized galls, instead of growing in the regular pattern.

Prevent by rotating Brassica crops, as disease spores can live in the soil for a few years. Solarizing the soil (by laying clear plastic tarp over the soil surface for up to 6 weeks in the hottest time of year) can help kill some of the spore population. Raising the soil’s pH level to increase alkalinity can also help.

Learn more: to help with diagnosing and treatment, take a look at this helpful page from Cornell University.

Powdery Mildew can be an issue for cucurbits, beans, and some flowers. It is a grey/white “powder” that growth on the surface of leaves and on the stems. At a later stage, it can turn leaves and full plant brown and black. (Downy mildew is sometimes confused with powdery mildew because of their similar names, but it’s a different ailment that shows up in cooler times of year like spring and fall.)

Prevent by improving air circulation via pruning or staking, promptly removing any diseased foliage, and watering only in the morning and never overhead. Gently wiping the affected leaves in the first half of the day may also help disrupt the spore cycle.

Learn more: to help with diagnosing and treatment, take a look at this helpful page from Cornell University.

Mosaic Virus affects Nightshades as well as beans and causes marbled green and yellow pattern on leaves or veins. Early signs to look for are curled or wrinkled leaves and slow growth.

Prevent by keeping pest populations down (put row covers on vulnerable crops) , as some insects can help the spread of this virus from plant to plant, weed frequently and thoroughly, and avoid handling plants when wet.

Learn more: to help with diagnosing and treatment, take a look at this helpful page from Cornell University.

Fusarium Wilt can attack the Nightshade family, causing leaves to turn yellow. First symptoms are often seen on the lower and older foliage. As it progresses, young new growth will be affected too.

Prevent by controlling pest populations (especially cucumber beetles), and solarize the soil if you’ve detected signs of wilt in the past.

Learn more: to help with diagnosing and treatment, take a look at this helpful page from Cornell University.

Verticillium Wilt acts similar to Fusarium and also affects the Nightshades. First signs of Verticillium show up at the tips of branches (yellowing, drying) and then move toward the central stems. It’s common for symptoms to first show up on one section or half of the plant.

Prevent by controlling pest populations (especially cucumber beetles), and solarize the soil if you’ve detected signs of wilt in the past. Rotating crops can help reduce this fungus, but most likely won’t cure the issue.

Learn more: to help with diagnosing and treatment, take a look at this helpful page from Cornell University.

Blossom end rot is an issue of insufficient calcium during fruit formation in Nightshades. More information on detecting and dealing with it can be found in Erin’s Troubleshooting in the Tomato Patch article.

Damping off can devastate young seedlings. Take a look at Doug’s article on Transplanting and Troubleshooting to defend your newly germinated seeds against it.

Many of the resource links mentioned above lead to Cornell's Vegetable MD page - an extensive online resource for Plant Pathology and Disease Diagnostics. It's a great place to start researching if you think you have a sick plant on your hands!

This blog is provided by the Hudson Valley Seed Library, a small group of dedicated growers and plant lovers working to provide good seed to gardeners and small farmers. Your purchases support our work. Thanks!

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