Master Gardener: Herbicide drift damage looks unsightly but does not last long in tree life

Chris Himmelwright
Pratt Tribune
These white oak leaves show signs of herbicide drift damage. Though unsightly, the tree not suffer long-term damage.

Curled and cupped leaves on landscape trees may be caused by herbicide drift at this time of year. While there are some insects that can cause these symptoms (margin or vein pocket gall on pin oaks, or high aphid populations on young leaves), the most common cause is herbicide drift, or volatilization. The usual culprit is a phenoxy-type herbicide, of which 2,4-D is the most commonly used. Drift is caused when tiny spray droplets are carried by wind to off-site and off-target plants. This type of damage commonly occurs when an agricultural field is close to a residential landscape, and drift reduction methods are not followed, like accounting for the wind, and using uniform droplet or large droplet nozzles, and lower pressures.

Volatilization is a different problem altogether, and almost impossible to trace back to a source. Some herbicides, particularly the ester formulations of 2,4-D and related chemicals are prone to vaporize, and move off site. The conditions that promote volatilization (high humidity, low wind speeds) are different than conditions that promote drift (high wind speeds). Sometime the damage is caused by the homeowner themselves, spraying for weeds in their lawn.

The various oak species are quite sensitive to herbicide exposure, especially when the new leaves are just expanding. It is the time-sensitive nature of exposure that will lead to normal leaves being found on the same twig as badly distorted leaves. Redbud is another tree species that is very sensitive to herbicides. However, the presence of twisted and cupped leaves on your tree does not mean that tree will die. If most of the leaves remain green, and if new leaves emerge without symptoms, the exposure was not severe enough to do any real harm. This is a recurring problem, due to agriculture being the dominant land use in Kansas. Fortunately the damage, although striking visually, is usually superficial, and the tree will grow out of it in time.

Bitter Cucumbers

A bitter taste in cucumbers is the result of stress that can be caused by a number of factors, including heredity, moisture, temperature, soil characteristics, and disease. Most often this occurs during the hot part of the summer or later in the growing season. Two compounds, cucurbitacins B and C, give rise to the bitter taste. Though often only the stem end is affected, at times the entire fruit is bitter. Also, most of the bitter taste is found in and just under the skin. Removing the stem end and the skin can often help salvage bitter fruit. Bitter fruit is not the result of cucumbers cross-pollinating with squash or melons.

These plants cannot cross-pollinate with one another. Often newer varieties are less likely to become bitter than older ones. Proper cultural care is also often helpful. Make sure plants have the following: – Well-drained soil with a pH between 6.0 and 6.5. Plenty of organic matter also helps. – Mulch. Mulch helps conserve moisture and keeps roots cool during hot, dry weather. – Adequate water especially during the fruiting season.

Cicada Killer Wasps

These large (1 1/3 to 1 5/8-inch long) wasps fly slowly above the ground. Cicada killers have a black body with yellow marks across the thorax and abdomen. Wings are reddish-orange. Although these wasps are huge, they usually ignore people. Males may act aggressively if they are threatened, but are unable to sting. Females can sting, but are so passive that they rarely do. Even if they do sting, the pain is less than that of smaller wasps such as the yellow jacket or paper wasp and is similar to the sting of a sweat bee. The cicada killer is a solitary wasp rather than a social wasp like the yellow jacket. The female nests in burrows in the ground. These burrows are quarter-size in diameter and can go 6 inches straight down and another 6 inches horizontally. Adults normally live 60 to 75 days from mid-July to mid-September and feed on flower nectar and sap. The adult female seeks cicadas on the trunks and lower limbs of trees. She stings her prey, flips it over, straddles it and carries it to her burrow. If she has a tree to climb, she will fly with it. If not, she will drag it. She will lay one egg per cicada if the egg is left unfertilized. Unfertilized eggs develop into males only. Fertilized eggs develop into females and are given at least two cicadas. Cicadas are then stuffed into the female’s burrow. Each burrow normally has three to four cells with one to two cicadas in each. However, it is possible for one burrow to have 10 to 20 cells. Eggs hatch in two to three days, and larvae begin feeding on paralyzed cicadas. Feeding continues for four to 10 days until only the outer shell of the cicada remains. The larva overwinters inside a silken case. Pupation occurs in the spring. There is one generation per year. Cicada killers are not dangerous, but they can be a nuisance. If you believe control is necessary, treat the burrows after dark to ensure the female wasps are in their nests. The males normally roost on plants near burrow sites. They can be captured with an insect net or knocked out of the air with a tennis racket during the day. Carbaryl (Sevin) or permethrin may be used for control.

*Adapted from Kansas State Horticulture Newsletter