Powdery mildew? Curling leaves? How to solve common summertime garden problems!
Guest Contributor: Cassey Anderson, CSU Horticulture Agent
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Is your summer vegetable garden beginning to sputter? Read on for tips for diagnosing and solving common garden problems. I’m dividing the topics into two categories: Biotic and Abiotic. Biotic problems mean those issues that arise due to a biological, or living agent, whether it be insect, disease, or human! Abiotic are those that are outside of the above category, so can be physiological, environmental, or cultural in origin. Sometimes the line can be a little less than distinct between the two as we’ll see in several examples. Let’s get sleuthing.
This can show up on many vegetable garden plants including squash, cucumber, beans, even peas and carrots can be susceptible although at least here in Colorado we don’t see a lot of that. Typically, powdery mildew begins to make an appearance mid to late in the growing season. It is especially prevalent in gardens that are planted closely, and those that are watered with overhead sprinklers. Planting with adequate spacing and watering the soil not the plant are two great ways to prevent the onset of the disease. Powdery mildew is a fungus which grows thin layers of mycelium along the surface of the leaf or fruit (although growth on fruit is less common).
Be aware that some varieties of squash or zucchini have patterns on them that may look similar to powdery mildew. If you aren’t sure, you can send a picture to your local Extension office or you can look for patterns vs. a more random distribution. Patterns are likely natural, more random is more likely to be powdery mildew.
If your garden succumbs to powdery mildew every year in your cucurbits, your melons, squash, cucumbers etc. there are a few different management options. You can trellis your vine crops and grow them vertically; this improves air flow and reduces ambient humidity. You can also remove the oldest leaves as the plant grows, leaving 5-7 of the youngest leaves at any time. Finally, if summer squash is the disease-ridden culprit in your landscape, you can succession plant, plant new squash about a month after your first crop, rogue the first set out once powdery mildew begins to establish.
Early Blight in tomato and potato
A very common disease, the same one that caused the Irish Potato Famine in Ireland, shows up regularly in our tomatoes, especially those that have come from saved seeds if proper sanitation practices weren’t followed. Symptoms can include brown spots on older leaves, brown concentric rings on stems, leathery/black spots on fruit which may drop from the plant. To manage you can plant resistant varieties, be sure to succession plant (at least two years between using the same soil), increase airflow. You can also remove leaves with leaf spot and dispose of them outside your home compost system (landfill or commercial composting facility). Fungicides are rarely effective in a home setting and are not usually recommended.
Tomato spotted wilt virus
Another of the diseases that can impact tomatoes, tomato spotted wilt virus is another common disease seen in home gardens. This disease can be transmitted by an insect called a thrip, when it feeds on the tomato it can infest the plant with the TSW virus. Leaves may develop a cupped appearance, with the bottoms becoming bronze and then dying (leaving brown or black tissue). Most typically it can be seen on fruit with concentric rings developing across the fruit. Fruit is fine to eat but may have a poor flavor. It is best to purchase resistant varieties if you’ve had issues in the past. Pull and dispose of the infected plant.
Blossom End Rot
Blossom End Rot occurs in quite a few plant species including tomatoes, peppers, cucumbers, zucchini, squash etc. We often begin to see it as plants first ripen in the early summer and into mid-summer. While it is technically caused by poor calcium in the fruit, this does not necessarily mean that there is insufficient calcium in the soil. Crushing up eggshells or adding calcium to water is not likely to rectify the issue. Rather, it is good to practice good “cultural care” by this I mean you want to make sure you are watering, mulching, and fertilizing the plants as they need to be cared for. Erratic watering and cold soils lead to most blossom end rot issues, so look to your hose and your temperatures before amending with nutrients that are likely not lacking.
Pollywogging / distorted growth/poor pollination
Often found in beans or cucurbits, this can be caused by several different issues. First off, if you saved your seed but did not control for cross pollination you may have some interesting hybrids on hand. Cross pollination issues will only show up in fruit grown from saved seeds, not from those that cross pollinate this year. Rather it will show up if the seed is saved and planted in the following growing season. However, far more commonly distorted growth is caused by poor pollination. If a bean, cucumber, or zucchini is insufficiently pollinated and continues to grow you may see one half of the fruit mature, but the other remain small.
A good way to ensure distorted growth does not occur is to encourage pollinators throughout your garden. Avoid spraying insecticides unless necessary and grow flowers throughout your space to feed your pollinator friends.
Can have many causes but the most common are temperature, irrigation issues, and herbicide. Cool and warm temperatures can cause strange growth in leaves. Irrigating too much, too little, or erratically can also lead to leaf curl. If soil dries out too much, or is too saturated, leaves may begin to curl. Finally, some herbicides may cause cupping or curling or other distorted growth. Be cautious when purchasing manure, mulch straw etc. as one particular herbicide, Aminopyralid, can persist in these materials and may cause problems for your vegetable garden growth. If you suspect you have herbicide in your manure or your mulch do a test growth, if distorted growth appears remove if possible. Check out https://newcropsorganics.ces.ncsu.edu/2010/08/herbicide-carryover-in-manure-last-of-the-tomato-study-results/ for details on herbicide issues in vegetable crops.
As always, reach out to your local Extension office with additional questions and for further resources. Happy Gardening!
Gardening in Colorado? Check out our Colorado Vegetable Guide https://growgive.extension.colostate.edu/colorado-vegetable-guide/ for more crop information on all of the above plants.
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