Pest Alert

Aug. 30, 1998

Welcome to Pest Alert. Categories for topics are as follows, H - Herbaceous plants and flowers, W - Woody Plants, V - Vegetables, F - Fruit and L - Lawns.


W GANODERMA SHELF FUNGI (the fruiting structures) are appearing along the lower trunks of trees, particularly declining honeylocust throughout the state. The shelve-like fungi have a smooth, varnish-like coating on the top and are blood red to blackish red. The underside is white. The presence of the fruiting structures is an indication that root rot is occurring. The tree should be inspected by an arborist to determine if it is in danger of falling.

V,F,H SANITATION IS THE KEY to the control of many of the diseases we are now seeing on many vegetables, flowers and ornamental species. Diseased vegetable plants are often best managed by simply removing them from the garden. Many diseases overwinter on infected debris from the previous season. If this debris can be removed, buried or composted, most of these pathogens will be killed. This can mean significantly fewer disease problems next year, at least early in the season. Keep in mind that while many of the disease pathogens will be killed during composting that will only occur if the compost pile is active and generating heat in the range of 140F or higher. Small debris piles close to the garden will usually not generate adequate heat to kill pathogens and may even act as a source of future problems in the garden.

W SULPHUR SHELF MUSHROOMS (Laetiporus sulfureus) are beginning to appear on trees in the eastern half of the state. The large (5 to 10 inch) fungus is formed as many overlapping, fan-shaped shelves that vary from a bright sulfur yellow to orange. The fungus usually appears along the lower trunk of declining trees. The presence of this fungus is an indication that the tree is extremely decayed and is highly susceptible to failure. Trees on which the fungus appears should be carefully evaluated as to their stability. The sulphur shelf mushroom is also delicious when properly picked and cooked. However, never eat any mushroom that has not been personally identified by an expert. Mistakes in identification can have deadly results!

W WALNUT ANTHRACNOSE is showing up in eastern parts of South Dakota. The leaf symptoms are circular brown lesions that form on the underside of the leaflets. Leaflets with many lesions become yellow, curl and fall prematurely. Since the only a few leaflets on a leaf (and black walnut leaves may have 15 to 23 leaflets per leaf) may become infected, the leaf may appear "tattered" at this time of year. The disease is not a serious threat to the health of the walnut. No controls are necessary nor are they appropriate at this time.


F APPLE MAGGOTS or the "railroad worm", as it is called, has caused apples to be "dimpled" where the egg has been laid. Small brown streaks will be seen in the flesh of the apple where the maggot has fed. Infested fruit, while unattractive, is still edible but has a much shorter storage life. Once the maggots are in the fruit, no treatment is possible. If apples are infested with apple maggots, they can still be used but will not keep very long. Apply protective sprays of malathion, diazinon, Imidan or use a combination orchard spray to reduce infestations beginning in mid-July next season.

L DAMAGE FROM WHITE GRUB INFESTATIONS in lawns begins to appear this time of year. Symptoms include a general browning of the turf similar to severe drought stress. This is due to the severing and consumption of turfgrass roots by the final larval instar stage of certain Scarab beetles, such as May/June beetles, Masked Chafers, and Black Turfgrass Ataenius. With little or no roots, the turf cannot take up water and is no longer anchored in the soil. Large patches of turf can be easily lifted from the lawn. Oftentimes, damage from foraging animals such as skunks, raccoons, moles, and birds is more severe than actual grub damage. Rolling back the sod should reveal a cream-colored, C-shaped grub with a tan to brown head and three sets of prolegs. If populations are less than 8 to 10 per square foot for Masked Chafers or 3 to 5 per square foot for May/June Beetles, persistent watering may allow turf survival without the use of insecticides. If chemical treatment is warranted, Dursban or Diazinon can be applied now. Be sure to follow insecticide applications with 1" of water in order to move the product into the soil where the grubs are feeding. Since grub populations in the lawn are usually concentrated in certain areas, scouting for these areas and spot treating can reduce insecticide amounts. If populations are present this year, consider using one of two new products, Merit or Mach 2, next year. These products have low mammalian toxicity, are more environmentally friendly, and have season-long residual activity when applied in Spring. Don't apply Merit or Mach 2 this late in the season since their mode of action affects growth regulation between larval instar stages, and won't be effective.

V,F HOLES IN FRUIT of various types has been a big problem this year in the vegetable garden as well as the fruit plot. Tomatoes have been eaten by a wide variety of pests including grasshoppers which tend to prefer eating the ripening fruit over the foliage. Their damage will typically be in a small area on the fruit and may extend into the fruit up to about a ½" or so. Tomato hornworms will also eat holes very similar to the grasshoppers but will generally be eating more foliage than fruit and they also seem to prefer green fruit over ripening fruit. Hornworms will often eat a large portion of the young fruit they feed on. Tomato fruit-worms will also eat fruit as they bore through various parts of the plant. If fruit is close to the ground or actually in contact with the soil, several other pests may eat holes including slugs, wire worms, and other beetles. Slugs make rather ragged holes and will leave a slime trail behind. Wire worms make quite small holes about the size of a pencil lead.

The best control for damage to the fruit is to control pests when possible, but you must be very careful to pay attention to harvest intervals for the insecticides you may use. Typical control strategies include hand picking for hornworm or insecticides for chewing pests such as Sevin, malathion, diazinon, or rotonone. Some garden baits are available. Slug baits will contain the molluscicide metaldehyde and may also contain Sevin. Grasshopper baits are also available. A better approach with tomatoes is to harvest the fruit at the first signs of ripening and allow the fruit to continue to ripen indoors away from the pests.

Raspberries and other fruit are also being eaten by grasshoppers and other pests. Grasshopper damage is characterized by the removal of the surface of the small fruitlets which exposes the seeds. Apples are being eaten by grasshoppers too but the more likely pest is birds in this case. Birds are especially attracted to fruit that is beginning to show some color. Various scaring devices are available to help keep birds away or bird netting may be used. Various hornets and wasps may also be found in the apple orchard but these will generally be attracted to fruit that is already damaged by some other pest.

Once fruit has been damaged by one of these pests, the fruit may develop a rot or become further damaged by picnic or sap beetles. These small black spotted beetles will attack many types of fruit that is over-ripe, damaged or beginning to decay. The best control for these annoying pests is to clean harvest and remove all damaged or over-ripe fruit and vegetable from the garden.

W PEAR SLUGS also known as pear sawflies larvae are beginning to appear across the state. The larvae are slug-like, dark olive-green and slimy. They can be found feeding on the upper leaf surfaces of plums, cotoneasters, mountain-ashes and chokeberries. Heavily infested leaves may have everything but the major veins consumed by the insect. The larvae can be controlled with an application of Carbaryl or Malathion.


L LAWN WEED CONTROL? If your lawn is heavily infested with annual summer grasses, such as crabgrass, goosegrass, or foxtail, it is too late in the season to control them. These warm-season annuals will die with the first frost anyway. Consider using a pre-emergence herbicide next May for control. On the other hand, it is too early to begin treating perennial broadleaf weeds such as dandelion, plantain, white clover, and ground ivy. Applications made in early October will provide the best results. Probably the only recommended use of herbicides in lawns at this time of year would be the non-selective herbicides, such as Roundup or Finale, for turf renovation or reestablishment.


L  AS EARLY AUTUMN APPROACHES, lower nightime temperatures and lower humidity will help reduce summer lawn diseases. Applying a complete fertilizer at the rate of 1 lb. N per 1000 square feet will give the turf a "shot in the arm". If you haven't aerified your lawn for several years, now would be an excellent time to perform this important cultural practice. Hollow tine aerification breaks up compaction, reduces thatch, increases water infiltration, and allows increased gas exchange between the atmosphere and turfgrass roots. Allow the soil cores to dry, then drag a mat or piece of chain length fence over the lawn to break them up. If your lawn is thin, overseed with a broadcast or drop spreader before breaking up the plugs.

F APPLE FRUIT DROP has been a big complaint this year. Fruit drop may occur any time during the summer but is more common in late May or June. Fruit drop at this time is common because the fruit that was not completely pollinated will often drop before it develops very much. Fruit drop later in the season usually results from some type of damage to the fruit like apple maggots, coddling moth, plum curculio, damage from disease like scab or powdery mildew or from mechanical damage like hail. There is no real treatment at this point other than to do a better job of preventing damage next season.

W FALL COLOR CHANGES WILL BE STARTING SOON. Brilliant fall colors are not a common occurrence throughout the world. In fact, there are really only three regions, North American east of the Rocky Mountains, eastern Asia including central and northern Japan and southwestern Europe, that are known for their fall color changes. Here in South Dakota we have only a few areas where the fall colors come in a wide array of reds and yellows, Spearfish canyon, Sica Hollow and Newton Hills. In most of the other areas of the state the fall colors are limited to yellow. Yellow is a very common fall color for trees. The yellow fall coloration comes from two yellow pigments, carotin and xanthophyll, that are usually masked by the green chlorophyll. As chlorophyll production declines in the fall, these other pigments begin to stand out. Red fall color is much rarer in trees. This color is due to the production of a pigment called anthocyanin which results from the accumulation of sugars and tannins in the leaves. The intensity of red fall color is partially dependent on the weather conditions necessary for sugar production. The red fall color is most brilliant when the fall weather is cool, sunny and dry. Trees noted for their brilliant red fall color include Amur maple (red to yellow), red maple, sugar maple, serviceberry, Ussurian pear and red oak. There also are cultivars of white ash, 'Autumn Purple', and buckeye, 'Autumn Splendor',that have brilliant purple to red-orange fall color. Most of the other trees found in the state, such as aspen, birch and cottonwood, have yellow fall color.

W FALL IS A GOOD TIME FOR PLANTING. Many homeowners believe that landscaping has to be done in the spring. But fall is an especially good time to complete those landscape projects around the house. The typical fall combination of warm, moist soils and cooler air temperatures reduces transplanting stresses and speeds recovery. And added bonus, September garden center prices are usually at a seasonal low as managers try to reduce the stock to carry over the winter.

V ROTTING, OFF-COLOR & MALFORMED TOMATO FRUIT has been common this year, especially in wetter areas of the state. In most cases the fruit rot is due to either Late Blight, Early Blight or Anthracnose. Late blight will cause fairly large areas of the fruit to look black but remain firm until the fruit ripens when it will soften and become watery. Early blight will generally attack the fruit at the stem end of the fruit causing darkened, rotting areas that have the distinctive target pattern associated with Alternaria infections. Anthracnose will cause small, circular, depressed areas to develop on the fruit which soon soften and spread through the fruit. Blossom-end rot has also been common. Here a calcium imbalance in the fruit results in a blackening of the blossom end of the fruit. This problem is usually more of a problem on the first fruit to ripen and if the tomatoes have not been watered properly. (See earlier issues of Pest Alert for more on blossom-end rot.)

Some gardeners have complained about fruit that does not ripen evenly and has hard greenish or whitish areas in the flesh. This is often a physiological problem called "persistent green shoulder". Related conditions described in some references include "internal browning" and "graywall". In most cases this severity of these problems will vary depending on the season and the variety of tomatoes grown. Some references also are made to involvement of certain bacteria or viruses. There is no treatment for these problems other than to try to provide good growing conditions, select good varieties and plant more than one to help insure a harvest.

Malformed fruit can develop from a variety of causes including exposure to chemicals like herbicides, unusual weather and the variety of tomatoes that are grown. One common problem is called "catface" which is usually the result of exposure to herbicides during flowering. The growth regulator effects of chemicals like 2,4-D cause uneven development of the tissue inside the fruit resulting in malformation of the fruit. Some varieties develop a nice smooth bottom and top to the fruit while others are known to have irregular shapes.

W WHILE FALL IS THE BEST TIME TO FERTILIZE YOUR TREES AND SHRUBS, now is a little too early. Though some homeowners are out fertilizing their trees now, it is best to wait until after the first hard frost (temperatures down to 28 degrees F). After that time the tree is going dormant and the fertilizing will be absorbed and used for next year's growth. Applications made after the first hard frost will not reduce winter hardiness.

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Most recent revision Tuesday, Sept. 1, 1998 by David F. Graper.