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ISSUE 2  May 10, 2001

 

TREES

Forest Tent Caterpillar

Small pockets of forest tent caterpillars (FTCs) have been consistently causing problems in North Dakota since 1997. Most of the infested areas have been severely defoliated once during the last four years and defoliation has been occurring in scattered clumps of trees. Since defoliation is early in the year and healthy trees will usually develop a second flush of leaves, tree health is usually not affected. However, the insects can become a nuisance during early to mid June.

Substantial defoliation of hardwoods by FTC has been reported in Canada, Minnesota, and eastern North Dakota in recent years. Basswood and aspen have recently been defoliated most (moderate to complete defoliation) in North Dakota, while bur oak, boxelder, and green ash have usually been lightly defoliated. Most of the defoliated oaks and basswoods refoliated quickly, while aspens were slow to recover. Healthy green ash should refoliate by mid summer. Outbreaks may last one to four years in North Dakota. Parasitic flies (also called "friendly flies") are apparently important in the collapse of individual FTC pockets in North Dakota.

Forest tent caterpillars overwinter as fully developed larvae in egg cases which are laid in masses encircling small twigs. The tiny caterpillars emerge in spring and can often be found first near the egg masses. Unlike other tent caterpillars, FTCs do not produce large, unattractive webs. The caterpillars do congregate on stems and branches during the day. Forest tent caterpillars feed on ash, aspen, basswood, birch, cottonwood, elm, maple, oak, poplar, and other hardwoods. As the larvae enlarge, keyhole_shaped spots along their backs and broad bluish lateral bands become evident. These markings make identification relatively simple.

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Management. It is difficult to determine how much damage the forest tent caterpillars will cause this year and during the next few years in the state. Since the adults are moths that are attracted to lights, shutting off yard lights from late June through mid July may reduce the number of egg-laying adults in areas where the larvae could become a nuisance the following year. This may reduce defoliation the following year. If only a few caterpillars are found, they can be picked from trees by hand. When FTCs are migrating to noninfested trees, they can be stopped with Tanglefoot or other sticky material. The sticky material must be checked on a daily basis. If treatments do become necessary, Bt can be effective when applied early. Since the insects are already feeding, this product should be applied as soon as possible for best results. Bt works well to control young caterpillars, while permethrin, pyrethrins or other insecticides are needed for older larvae. Always follow pesticide labels. Ensuring that trees have adequate water can help trees recover from early season defoliation; however, do not fertilize trees during FTC outbreaks.

Marcus Jackson
Extension Forester

 

DANDELIONS ARE COMING UP ALL OVER!

Questions are coming in concerning dandelions: "If I cut my grass short enough to remove the dandelion flowers, will that stop them from setting seed?" How I wish that did it! They will only set their flower heads lower, so you might as well cut the grass at the correct height to help make it competitive against these and other weeds - which is 2.5 to 3.0 inches. Cutting the turf shorter in order to catch the dandelion flower will only thin the turf making it vulnerable to wear, insect damage, more weeds, and environmental stresses. Instead, use the blooms as a target for Trimec, a systemic herbicide. Don't kid yourself that because you see the flower stems and leaves curling, that you have seen the last of dandelions in your lawn! They will be back in about 2 weeks, so another application is necessary at that time.

Finally, the absolute best time to apply any herbicide to control broadleaf weeds in your lawn is in the late summer or early fall - just before Labor Day weekend. The lawn should not be watered or mowed for two days after application. Keep in mind that dandelion seeds can be carried miles by a slight breeze, with each plant having the capability of producing over 15,000 seeds. Will dandelions ever be completely out of our lives? Not likely. You might try making wine with the blossoms, growing them as an alternative crop for salad fixings, or to sell to herbal companies to make into diuretic pills!

Ron Smith
NDSU Extension Horticulturist and Turfgrass Specialist

rsmith@ndsuext.nodak.edu

 

SPRING YARD AND ACTIVITY

After a long winter, the sight of green grass is a welcome relief to many. Warmer temperatures bring renewed excitement for planting and lawn care. Before diving in, however, it is wise to look ahead and use some caution. Lawns need attention in the spring to be their best over the summer and fall. It is really best to wait until temperatures get into the 50's (fahrenheit) to begin much activity on the lawn to help the grass recover from winter. Once temperatures do warm up, rake up leftover leaves and debris, and dead grass that has accumulated. Dead patches, killed by pet activity, snow mold, etc. should be re-seeded. Rough up the soil in these areas, sow Fusarium-resistant seed, and cover with a light dressing of top soil. Be sure to plant shade tolerant seed in shady areas and seed intended for sunnier areas if there is no shade cover. Avoid walking in these areas and keep them moist but not too wet. Generally speaking, aerating and/or de-thatching is good for a lawn. If patch diseases are a problem, aerating each spring will help alleviate symptoms and reduce pathogen populations. Sodded lawns, especially those on clay-based soils, are particularly susceptible to patch diseases and will benefit from annual aerating regardless of whether disease is a problem. This will help establish a deeper root system and prevent disease. De-thatching is beneficial but only if it is well timed. Since de-thatching can be cause damage to the crowns of the grass, it is best to de-thatch when there will be at least a week of temperatures below 75-80 degrees. In general, research shows that fertilizing in the fall with a slow release nitrogen gives the best results. If you didnít fertilize last fall, and would like to this spring, make the application after cutting the grass once or twice. Remember these products are activated by rain or irrigation so be patient if results are not immediate.

Even though the corner stands and greenhouses are out and very busy, be cautious about planting many flowers. There is still a danger of low and freezing temperatures at night. Perennials should be okay this time of year, but annuals may need to be protected or brought indoors if temperatures do get down to freezing. Major pruning should have been done earlier in the year; however, dead areas in evergreen shrubs and bushes may be pruned out but only after the new growth comes out this year. Pruning all the brown material out now will cut off some healthy buds that might have provided new growth. If winter burn has taken its toll and after cutting out the brown material, there is not enough left to be aesthetically pleasing, it may be best to remove the plant and replace it with a healthy one. Be sure to inspect bulbs that you may have taken indoors for winter. Do not plant any that are mushy and soft or discolored. When selecting plants from a greenhouse, be sure to inspect the plant parts. Select only those that have intact flowers and turgid, green foliage. Also be sure to select plants appropriate to the area where they will be planted (shade tolerant or sun loving). As much as possible, try to plant into well-drained soils. Augmenting existing soils with peat can help improve drainage. Now is a good time to separate perennials that have become overgrown. And you can always call or email the Plant Diagnostic Lab if questions come up: 701.231.7854 or diaglab@ndsuext.nodak.edu.

Cheryl Biller
diaglab@ndsuext.nodak.edu


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