Leaf Galls Look Worse Than They Are

If you've noticed balls, knobs, lumps, or warts of various shapes, sizes and colors on trees and other plants, you've discovered galls. Galls develop from plant tissues that have been irritated and/or stimulated by a parasitic organism. Galls are believed to be caused by powerful plant-growth regulatingchemicals produced by the parasite. If the parasite leaves the host or dies, normal cells are again produced.

Aphids, midges, wasps or mites cause about 95 percent of the known types of galls. Bacteria, fungi and viruses cause the remaining 5 percent.

Most galls are found on leaves such as maple bladder gall or hackberry nipple gall. These bumps, either on top or bottom of the leaf, are nothing but plant tissue. Try to remove the gall without leaving a hole in the leaf. It's impossible.

Although the galls are common and easy to see, they are seldom important enough to control. In general, insect- and mite-produced galls disfigure twigs and foliage but rarely seriously affect the health and vigor of the host plant. Once gall formations become noticeable, the insect or mite causing the injury is protected from chemical sprays. It is too late to exercise any control other than removing the infested part.

In short, it's an appearance problem more than anything else. Trees are seldom harmed.

Hand removal is only practical when there are just a few galls present. Chemical sprays are seldom warranted where gall infestations are light.

Plants with heavy infestation, such as oaks with horny or gouty oak galls which affect twigs, or those that are tremendously unsightly can be treated. Refer to the Home, Yard and Garden Pesticide Manual for current recommendations. Be sure to read and follow label directions when applying any chemical.

Wilt Symptoms in Cucurbits

Have you noticed your cucumbers or other cucurbit crops suddenly wilting and then dying? Cucurbits, also commonly referred to as vine crops, include cucumber, winter melons, cantaloupe and muskmelon, watermelon, summer and winter squash, and pumpkins. There are several potential causes of these wilts, and usually it is too late to cure the problem once it has occurred. But if your vines have wilted and died, you need to take steps to prevent the problem from developing again.

One of the most common causes of wilt in cucurbits is a bacterial disease called bacterial wilt. Melon and cucumber are severely affected by bacterial wilt, whereas the disease is not as damaging to squash and pumpkin, and watermelons appear not to be affected by it. The bacterial wilt pathogen is entirely dependent on spotted and striped cucumber beetle for its transmission. The beetles carry the pathogen in their gut, which can then transmit to the leaves of cucurbits while the beetles feed. Beetle excreta may also contain the pathogen which can infect the plant through any type of wound. Because beetles are less active in wet weather, the disease is mostly spread from plant to plant on dry days.

Here is a simple way to identify whether bacterial wilt is present. Cut a wilted runner close to the crown–select a runner that is just dying, not one that is completely wilted or dead. Rejoin the two cut ends together for a moment and gradually pull apart. Sticky strands up to ¼ inch long and somewhat milky in color spanning the two cut pieces is a positive indication of bacterial wilt.

There is no cure for infected plants, and control of bacterial wilt depends on control of the cucumber beetle vectors. Since the infected beetles may overwinter as adults, they can transmit the disease as soon as they feed in the spring; so, early season control of cucumber beetles can reduce infection. Insecticides, whether organic or synthetic, are generally required to maintain good cucumber beetle control throughout the season. Immediately remove and destroy infected plants so that uninfected beetles do not become infected through feeding. Control all weeds in or near the garden in order to reduce hiding places throughout the year.

Cucurbits are also affected by a number of vascular wilt diseases caused by different forms of Fusarium oxysporum. Cucumbers, melons and watermelons are severely affected by the different forms of Fusarium wilt, but all forms are similar in their disease cycle, cause, and control. Each form of Fusarium wilt is soil-borne, is long-lived and persistent in the soil, and can be seed transmitted. Wilting of the plant as a result of breakdown and blockage of water-transporting structures characterize the diseases. Fusarium wilts can attack a plant at any stage, but mature, fruit-bearing plants infected earlier in the season often show the most severe symptoms and incur the heaviest losses–likely due to the increased demand for water during fruit development and maturation.

The use of resistant cultivars is the most practical means of controlling Fusarium wilts in melons and watermelons. Plant on new land whenever possible, and if not possible, avoid planting in the same soil for a minimum of 5 to 7 years. Crop rotation is considered ineffective because of the long survival of the fruiting bodies in the soil and the ability of the fungus to be present in or on the roots of a symptomless host, including weeds. Research has shown that liming the soil to pH 6.5 to 7.0 can reduce wilt. The optimum pH range for many of the cucurbits is between 6.0 and 6.8, so pH can be adjusted to suppress Fusarium without creating an unfavorable growing condition for the vine crop. Also, reducing the level of ammonium nitrogen in the soil, which tends to lower soil pH, can suppress the development of Fusarium wilts. You can accomplish this by using nitrate forms of nitrogen instead.

Another common cause of wilt in cucurbit crops is the squash vine borer, Melittia cucurbitae. The adult squash vine borer is an orange-bodied moth with black wings, and it lays its eggs on all parts of the plant except the upper leaf surface. Those that hatch on the vine usually remain in this location to feed, whereas those hatching on the leaf petioles eventually work their way to the base and enter the vine. With enough numbers present, the larvae can disrupt the physiology of the plant beyond its ability to compensate successfully for the feeding injury. Often, the first sign of infestation is wilting of the plant in the heat of the day while other plants remain upright. Summer squash derived from Cucurbita pepo and some winter squash derived from C. maxima are most preferred by adults for egg laying and most suitable for larval development. Some pumpkin derived from C. mixta, can be attacked when the more favored hosts are not present. Winter squash from C. moschata are not favored because of their unsuitability for larval development.

Insecticide sprays, whether synthetic or organic, are only effective if they are applied during egg laying so that when the larva hatches from the egg, it has an opportunity to make contact with a lethal dose. To determine when adult moths are present in order to time insecticide sprays, you can use shallow pans painted yellow and filled with water to attract and capture squash vine borer moths. Squash vine borers overwinter in the soil as pupa, and adults are capable of laying eggs about three days after emerging from the soil from the soil. Eggs hatch in 10 to 15 days, and larvae soon bore into the plant.

Early-planted crop tend to experience less injury, so early planting is recommended when possible.The more preferred species, like summer squash, can also be planted to act as a catch crop. The catch crop is then destroyed o sprayed, thereby protecting less preferred cucurbit species. The presence of frass, sawdust-like excreta, usually indicates the presence of a larva actively feeding. Many times, larvae can be killed or removed with a knife without severely affecting growth of the reamaining tissue. Lightly covering the vines near the base of the plant can also discourage egg layingnear more critically important tissue.

Managing Duckweed and Watermeal in Ponds

This time of year, duckweed and watermeal can be found on farm ponds–so you may get questions from clients on control measures.These free-floating plants can completely cover a pond. If this occurs for several summers, fishing quality may be reduced.

Duckweed plants are about ? to ¼ inch wide. Each plant will have a single hair-like root. Watermeal is smaller than duckweed and looks like tiny green seeds.

These plants are found in nutrient- rich ponds and can be spread from one pond to another by humans and by ducks or geese. During the fall, the weeds lose buoyancy and settle to the bottom of the pond. The next spring, when photosynthesis begins, they regain buoyancy and float back to the surface.

Non-chemical control of these two plants has limited effectiveness. Reducing the nutrients flowing into the pond helps but does not usually eliminate the plants. Mechanical skimmers will physically remove the plants, but the plants must be moved far enough away to prevent them from washing back into the pond.

Chemical control can be effective if the right products are used. Diquat, a contact herbicide, is effective on duckweed but generally not effective on watermeal. Diquat should be used as soon as the plants are seen. Several treatments may be needed during the growing season.

Fluridone is also effective on duckweed. Split treatments, about two weeks apart, are usually required. Fluridone is not a contact herbicide; if there is a heavy rain within 30 days, effectiveness may be diminished. It may also take some time to see results. Fluridone is generally effective on watermeal if correctly applied according to label directions.

Both products can be purchased through farm chemical suppliers. If used properly, these products will not harm fish or fowl. But, they cannot be used within ¼ mile of a potable water intake. Keep in mind when large amounts of aquatic plants are killed, especially when pond temperatures are high, there is a risk of oxygen depletion. As the plant material decomposes, oxygen is taken out of the water. In some cases, oxygen levels become too low for fish, creating a fish kill. Consider this possibility when trying to apply aquatic herbicides in mid- to late summer. As always, be sure to read and follow label directions on all herbicides.

For more information on duckweed and watermeal management, check out these online resources:

http://www.ipm.uiuc.edu/weeds/aquaticWeeds.pdf

http://www.btny.purdue.edu/pubs/APM/APM-2-W.pdf

http://ohioline.osu.edu/a-fact/0014.html

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Revised May 31, 2005