Cucumbers (Cucumis sativus) rapidly fill up any space they can be given, and if given the right amount of space with the right conditions, they produce an abundant crop yield. However, if cucumbers are subjected to less than ideal conditions, they will become vulnerable to insects and diseases which may decrease or kill the whole crop. One of the list of insects and disorders cucumbers are vulnerable to, black specks are a symptom of four: gummy stem blight, anthracnose, squash bugs or four-lined plant bug.
Gummy Stem Blight
Symptoms of gummy stem blight begin as tan or brown spots on leaves and finally progress into splitting stems and fruit rot aptly named black rot. When black rot sets in, the fruit becomes riddled with tiny black specks or water-soaked dark spots and collapses. Treatment for gummy stem blight involves removing all plant debris, improving drainage by amending beds using organic materials and staking or caging cucumbers. Avoid overhead watering and rotate crops using non-host plants — like corn — for two or more years to decrease the chance of cold-blooded gummy stem blight again.
Anthracnose Signs and Infection
When cucumbers are subjected to cold, rainy weather for over a couple of days in mid-to late season, there’s a possibility they’ll become affected by anthracnose. Signs of infection include salmon-colored spores, tiny black specks, black sunken cankers on fruit, and yellowish or water-soaked spots, which eventually enlarge and flip to brown and black spots. In severe cases of this fungus, destroy all plant debris and infected plants. The disease can be seed-borne, therefore purchasing seeds from a reputable source and rotating crops helps prevent the disease from recurring in following seasons.
Wilting leaves, speckles which turn yellow and brown or black and rotting fruit might signal a squash bug infestation. The brown, shield-shaped bug seldom attacks cucumbers, but if it does, the very best treatment options include handpicking bugs and dropping them in soapy water, and then crushing eggs. Lay out boards at the bottom of the cucumbers to entice squash bugs for crushing in the morning. Clear mulch from the foundation of the cucumbers to remove the shelter that the insects need. To further control a serious infestation, then combine handpicking with insecticidal soap software. Mix 2 1/2 to 5 tablespoons per 1 gallon of water, and then apply when the eggs have been hatching to kill young nymphs. Be sure to completely coat the base of the plant and undersides of the leaves. Wear gloves and protective clothing when applying and blending.
Four-Lined Plant Bug
Feeding damage from four-lined plant bugs — 1/2-inch long insects that resemble striped cucumber beetles — shows by 1/16-inch diameter black and brown sunken spots and holes in leaves. Most times, four-lined plant bugs go unnoticed since they quickly conceal under leaf or fall to the ground when disturbed. Their speed makes handpicking just a control choice for fast eyes and hands. Otherwise, control them together with applications of insecticidal soap. As per most instruction labels, mix 2 1/2 to 5 tablespoons of insecticidal soap per 1 gallon of water in a clean sprayer. Saturate the top and undersides of the leaves when the temperatures have been lower than 90 degrees Fahrenheit. Treat every four to seven days till insects are gone. Although insecticidal soaps are safer than several lawn chemicals, avoid issues like eye irritation by wearing protective eyewear, long pants, long sleeves, and gloves when spraying the cucumbers.