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Summer Good, Summer Bad

Posted: July 29, 2011

Summer may bring bountiful harvests of beans, sweet corn, cucumbers, tomatoes, and other produce, but it also brings its share of problems for the home vegetable gardener. The problems are not new, but a very wet spring followed by hot and droughty summer weather has presented some new challenges in the home garden this growing season.
Tomato Perfect

Tomato Perfect

Q: My tomatoes look black on the bottom. What is the problem and what can I do about it?

A: This is Blossom End Rot (BER). It is not a disease, but the result of insufficient calcium in the plant when the fruit is developing. The lack of calcium in the plant causes the blossom end (opposite the stem) of the fruit to become dark brown, leathery, and sunken.

The soil may be deficient in calcium. Usually, though, there is enough calcium in the soil, but the roots are unable to absorb it for a variety of reasons. Drought; drastic moisture fluctuations in the soil, the result of too much or too little rainfall; high temperatures; excessive nitrogen fertilization; rapid plant growth; or damage to the roots due to cultivation, are all possible causes for inadequate calcium uptake.

The solution is to make sure that you supply an adequate amount of moisture to the plant – tomatoes need 1 to 1.5 inches per week – during the growing season. Drip irrigation and straw or plastic mulch will help ensure even moisture to the plant while conserving water.

For a quick fix, you can put 1-2 tablespoons of hydrated lime over the root zone and water it in thoroughly. You can also try a calcium spray applied to the foliage (not the fruit). It’s important to follow the label directions, as you can burn the foliage if you apply too much or too often; the calcium spray won’t correct affected fruit, but it may help to prevent BER on fruit just beginning to develop.

These short term remedies are band aids, not a substitute for proper fertilization and watering. A soil test and good soil preparation this fall, along with sufficient water next summer, are the best solutions to BER.

Q: My cucumbers taste very bitter. What’s wrong and what can I do about it?

A: Bitterness in cucumbers increases when plants are stressed from drought, high temperatures, or poor fertilization. As with BER, the solution is to ensure an adequate supply of water to the plant – 1 to 1.5 inches per week – during the growing season. Use drip irrigation, or deep but less frequent waterings, combined with mulch to conserve moisture and keep the soil cooler. Sufficient water may lessen the bitterness in later fruit.

Cucurbitacin is the compound that causes bitterness in cucumbers; often it is concentrated in the stem end of the fruit, or in and just under the skin, and cutting away those parts removes the bitterness. But if the whole fruit is bitter, discard it; nothing will make it taste any better.

Many newer cucumber varieties have been bred to be “bitter-free.” Look for these cultivars – including Carmen, County Fair, Diva, Green Knight, Sweet Slice, Summer Dance, and Sweet Success – when selecting plants or seeds next year.

Q: I am finding brown marmorated stink bugs (BMSB) on the corn and tomatoes in my vegetable garden. What can I spray to kill them?

A: This is a question without an easy answer. According to the Maryland Department of Agriculture, “there is currently no quick or certain way for homeowners to control this pest, and there are no chemical recommendations currently available for homeowners to follow.”

For commercial fruit growers, the EPA recently approved emergency registration of two insecticides to help manage BMSB populations in commercial orchards for this season. Researchers are still working on developing effective and sustainable long-term control methods.

Most insecticides available for home gardeners are ineffective on BMSB. Many of them may only cause “knockdown” and not death, which means the insect recovers after a while, its body having metabolized the chemical compound. Many of the stronger insecticides are “broad spectrum,” killing bees, spiders and beneficial insects such as predators and parasitoids that may prey on BMSB. There is also evidence that BMSB are developing resistance to some insecticides, so that the chemical no longer has an effect on the insect.

For these reasons, insecticides are not recommended. But if you choose to try one, make sure it is labeled for the target pest (stinkbugs at least) and target plant, and read and follow the label directions for application. One relatively safe choice is insecticidal soap on early instars, or nymphs, which are more vulnerable than adults.

Deterrence methods to try for home vegetables and fruits include floating row covers; Surround, a kaolin-clay product for fruit; and hand-picking or knocking BMSB into a container of soapy water. There are many good websites and images available online to become familiar with the appearance of this insect at all stages of its lifecycle.