Not much takes the wind out of our sails like a wilted plant. When it's zucchini that had big, bold, green leaves just yesterday you might wonder what caused this drastic change overnight.
Zucchini is a prolific, easy-to-grow vegetable that produces harvests nearly all summer long. When a pest or adverse growing condition affects your crop, symptoms show up quickly; plants wilt and the large, palm-shaped leaves develop yellow spots or turn yellow.
Here are four problems that crop up in the zucchini patch and how to prevent or fix them.
Under Watering
Zucchini leaves often wilt down in the hottest part of the day. Soil moisture is the first thing to check before you start looking for pests or other causes. Zucchini are not drought tolerant and underwatered plants develop yellow leaves that eventually turn brown and dry up.
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When to Water Zucchini Plants
If your zucchini plants look droopy in the morning do a soil moisture check. Meters are available that give you a reading or you can poke your index finger into the soil. If it comes out dry, you need to water.
Zucchini need at least an inch of water each week. A layer of mulch helps keep soil moist and cool. Water at the base of your plants instead of overhead to discourage foliage problems that lead to wilting and yellowing.
Squash Vine Borer
The biggest menace to squash is the squash vine borer, (Melittia cucurbitae). This day-flying moth has a distinctive, black-spotted, orange abdomen and emerges in late June after overwintering underground.
Squash vine borers lay eggs singly at the base of your zucchini plants. The egg hatches into a brown-headed, white grub that bores into vines hollowing them out and preventing water and nutrients from reaching the leaves. Starting out, your zucchini plant may wilt only in the heat of the day. But when leaves appear wilted in the morning, yellowing soon follows and the plant will succumb and die. Signs of squash vine borer activity include a sawdust-like build-up at the base of the plant called frass.
How to Treat Squash Vine Borer
Prevention is often the best approach to insect pests and environmental issues. Starting in mid-June, try spraying the center and base of your plants with a pesticide formulated for grubs and caterpillars. Organic alternatives include diatomaceous earth and the deterrent BT.
Follow label directions for the frequency of treatment. Use a floating row cover to prevent egg-laying activity.
When the plant already shows signs of infestation, removing the grub can sometimes revive it. Use a sharp knife to slit open the top of the vine. Be careful not to cut through the bottom. Gently open the vine until you find the white grub. Scrape it out with your knife but try to limit damage to the vine. Bury the opened part of the vine under the soil and check to see if the plant recovers.
Squash Bugs
Squash bugs,(Anasa tristis), are as prolific as zucchini plants, themselves. That's because adult females lay reddish-brown eggs in clusters of 15 to 40 on the undersides of leaves. Sap-sucking nymphs hatch out in numbers and can damage leaves quickly causing yellowing and wilt. Adults also feed on developing fruits.
How to Treat Squash Bugs
Once they establish squash bugs are hard to get rid of. Prevention is the best approach and organic sprays along with hand-picking are more effective than harsh chemicals which can kill pollinators necessary for a healthy crop.
Practice good garden hygiene by removing debris at season's end and tilling soil either in late fall or early spring.
Check the undersides of leaves regularly and scrape off any eggs.
Place wooden boards around the zucchini patch. Squash bugs shelter underneath at night and can be hand-picked in the morning.
Horticultural oils sometimes eliminate newly hatched nymphs but are ineffective on adult populations.
Plant blue hubbard squash as a trap crop and hand-pick pests that congregate.
Squash Bug vs. Stink Bug
Squash bugs and stink bugs are similar in shape and size but stink bugs are a little wider and rounder. Squash bugs feed on cucurbits only while stink bugs are more often found on tomatoes and beans. Both pests can be treated with the same methods.
Powdery and Downy Mildew
Powdery mildew looks like white chalk dust on zucchini foliage and usually appears first on the newest leaves. It's an airborne fungus that thrives in high humidity even in dry weather. Downy mildew causes yellow spots to form between leaf veins and a brownish-gray fuzz on the undersides of leaves. It's caused by a pathogen rather than a fungus and appears in wet, humid weather.
Zucchini are less vulnerable to these pathogens than cucumbers and melons but can still be affected.
How to Fix Downy and Powdery Mildew
Adequate air circulation is critical to preventing leaf infections. Plant zucchini the recommended distance apart. You can even remove some leaves at the base to improve airflow within the plant.
An appropriate fungicide can work to manage powdery mildew once it sets in. For downy mildew use neem or horticultural oil.
Remove infected leaves early and treat the remaining foliage.
Remove and discard severely infected plants from the garden to avoid disease spread.
Bacterial wilt is caused by a bacterium, Erwinia tracheiphila, that causes plants to wilt and eventually die. You may notice leaves turning yellow and then brown before they wilt, or this may happen after. If the entire plant is wilting, this can also be a sign that it isn't getting enough water.
Overwatered zucchini plants often have yellowing leaves that may look wilted or lifeless. Despite this wilting appearance, the leaves often feel soft and bloated due to excess water. Zucchini plant roots of overwatered plants may become waterlogged, leading to root rot, further deteriorating the plant's health.
An all-purpose food like 10-10-10 is generally sufficient for zucchini plant needs. They contain plenty of nitrogen to facilitate healthy growth as well as necessary potassium and phosphorus to boost fruit production. You may use a water soluble or granule fertilizer.
Blossom-end rot is a physiological disorder that occurs on tomatoes, peppers, eggplant, and summer squash. On zucchini and other summer squash, the blossom end of the fruit begins to rot and within a short time the entire fruit has rotted. Blossom-end rot is caused by a lack of calcium in the developing fruit.
Verdict: Unless you have a magnesium deficiency in your garden, there is no need to add Epsom salts. Doing so could even be harmful to soil, plants and water.
Check the humidity levels around your plant. Tropical varieties love a little steam. You can provide humidity by using a humidifier, a diffuser (just add water and leave out essential oils), or simply move them to naturally humid rooms, like the bathroom. If these solutions don't stop the browning, investigate further.
One inch of water per week should suffice, but water more often if the weather is particularly hot and dry. Well-draining soil is a must—if it water pools and remains stagnant around the roots, they will start to rot. Avoid letting your soil dry out; this can increase the risk of blossom end rot.
Calcium is not taken in well by the foliage, so avoid a foliar spray. Calcium needs to go directly to the roots. Calcium carbonate tablets, or anti-acid tablets like Tums, can be inserted at the base of the plant. They will then dissolve and within a few hours, calcium will be available to the plant.
Yes, coffee grounds can be used as a natural fertilizer for plants, including zucchini. Yes, coffee grounds can be used as an addition to your compost or as a mulch around plants to provide nutrients and deter slugs.
A nitrogen-rich liquid fertilizer solution is the fastest way to add nitrogen to the soil but it risks leaching so fast is not always best. Using a slow-release fertilizer is more beneficial for plants in the long run.
An all-purpose N-P-K fertilizer like 10-10-10 will provide zucchini with sufficient nutrients. The fertilizer you opt for should provide enough nitrogen to promote vigorous foliage growth.
Adding coffee grounds directly to the soil as a fertiliser can be a good option. Coffee grounds are rich in nutrients, especially nitrogen. They also have some amount of other nutrients like potassium and phosphorous. Overall, this means that adding coffee grounds to your garden can work fairly well as a fertiliser.
Zucchini leaves often wilt down in the hottest part of the day. Soil moisture is the first thing to check before you start looking for pests or other causes. Zucchini are not drought tolerant and underwatered plants develop yellow leaves that eventually turn brown and dry up.
If you have zucchini leaves wilting, it's probably the vine borer. These are larvae of a moth. This particular moth has clear wings and is sometimes mistaken for wasps. The vine borer overwinters in cocoons in the soil and come out as adults in late spring.
You should always remove badly damaged, dying or yellowed leaves. They aren't contributing anything to the health of the plant and only serve to reduce that all-important airflow. But they you can go a step further, by removing any overlapping leaves. These are typically the oldest leaves lower down on the stem.
One inch of water per week should suffice, but water more often if the weather is particularly hot and dry. Well-draining soil is a must—if it water pools and remains stagnant around the roots, they will start to rot. Avoid letting your soil dry out; this can increase the risk of blossom end rot.
Zucchini thrives in a dry environment, so pop it into the crisper drawer whole, preferably in a plastic or paper bag with one end open for ventilation. The minimal humidity will keep it from going bad. Stored properly, it'll last one or two weeks, though you'll probably see the skin shrivel as the days pass.
Inconsistent watering, in particular allowing plants to dry out too long between waterings, will cause leaf edges and tips to turn brown. Excess salts can build up in the soil when too much fertilizer is applied which can also lead to brown leaf tips. Water and fertilize appropriately to prevent further browning.
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