ISSUE 2    May 11, 2006

LAWN INSECTS

Sod Webworms (Crambidae)

If you are seeing brown irregular brown spots in your lawn, look for the sod webworm larvae in the thatch. Larvae can be a 1/4 to 1 inches long and have a brown head with a grayish body with dark spots. Larvae construct a loose web, which leads to a silk-lined tunnel at the base of the plant where the larvae live. Larvae feed at night on the blades, roots, and crowns of grasses. The adult moths do not feed on lawns but are easy to observe flying over the lawn in a quick, jerky, zigzag flight before landing in grass again. Adult moths are about ½ to 3/4 inch long, light gray in color, and hold their wings over their bodies at rest. If your lawn is in good condition and growing vigorously, the presence of 2 to 3 larvae per square foot is probably not cause for concern. If your lawn is under stress (compacted, infrequently irrigated or fertilized), the presence of only one larvae per square foot usually indicates the need for treatment. Sod webworms are easily controlled with any of the presently registered insecticides. Mow and water lawn prior to application to aid penetration of insecticide. Alternatives to insecticides include some resistant types of turf (zoysiagrass and bermudagrass) and endophytic lawn grasses (perennial ryegrasses and fine-bladed tall fescues).

White Grubs

White grubs are the larval stage of June beetles (Scarabaeidae: Phyllophaga spp.). Grub damage in lawns occurs when larvae feed on the roots of grass causing brown patches. The size of the brown patch will vary depending on the number of larvae. Grub feeding separates the turf from the roots, so the turf can be rolled up like carpet. Grub damage is also common in pastures, corn, small grains, and garden vegetables. White grubs are easy to identify as a "C-shaped" larvae with a brown head capsule and creamy-white to transparent body color. When mature, grubs can be up to 1-inch in size. Most of the white grubs in North Dakota have a 3-year life cycle. Eggs are laid in the soil during May or June and the young grubs feed for a limited time in July or August before migrating down into the soil for the winter. Spring of the second season, grubs return to feed on roots throughout the summer and grow rapidly causing severe feeding injury. In the third year, grubs feed for a short period in May or early June before pupating in a belowground chamber. Pupae change into adults late summer and early fall and are ready to emerge the following year. Control of white grubs is based on timely application of soil insecticides. Similar to sob webworm control, mow and water lawn before insecticide application to aid penetration by the insecticide and to encourage grubs to move to a more vulnerable location close to the soil surface. Dethatching a lawn before applying an insecticide to control white grubs will also improve penetration of the insecticide. After application of an insecticide, irrigate lawn "slowly" to wash insecticide down into the soil where white grubs are. Be sure to avoid over-irrigating, which may cause the insecticide to runoff.

 

TREE & SHRUB INSECTS

Scales Insects

A large number of overwintering scales are present on many of our hardwood trees (maple, ash. elm, popular, boxelder, honeylocust). Soft scale insects secrete sticky honeydew, which causes problems when cars or picnic tables are underneath scale-infested trees. Honeydew also coats the leaves and promotes growth of black sooty mold fungi. Dormant oils can be applied before bud break to control the overwintering scale. Summer control of scale insects needs to be targeted at the crawlers (immature stage) that usually hatch from eggs in May or late June / early July depending on the species of scale insect. The oval, flat crawlers do not move very far from their hatching site. Egg hatch occurs for only a short period of time, so timing is crucial for effective control. To monitor for crawlers, place a white piece of paper underneath the branch and vigorously tap the branch to dislodge crawlers onto the paper. Crawlers can vary in color depending on the species, and are very small about the size of period on this page. Once crawlers settle and insert their coiled mouthparts into the plant usually 1-3 days, it will be difficult to dislodge them. Summer sprays of insecticidal soap or conventional insecticides at crawlers can be very effective in reducing the population. Conventional insecticides like orthene, sevin or malathion will also kill natural enemies of scale insects and ultimately could make the infestation worse.

Tent Caterpillars

Tent caterpillars have been reported feeding on fruit trees and other hardwood trees (Source: A. Ulmer). Tent caterpillars overwinter as eggs that hatch in spring. Caterpillars (larvae) feed for six to eight weeks and are about 2 inches long when mature. Caterpillars construct tent-like nests in the forks of trees. The web nests are conspicuous and unsightly. (Note: Forest tent caterpillar does not construct web nests.) Caterpillars defoliate and disfigure ornamental trees. When populations are high, whole trees can become covered with webbing and can be completely defoliated. Caterpillars feed outside of the web nests, which makes control with insecticides easy. Bacillus thuringiensis (Bt) controls young larvae, while synthetic insecticides or pyrethrins are necessary to control older larvae. Evening and early morning are the best times to spray before tent caterpillars congregate in their nests at night.

Janet Knodel
Extension Entomologist
janet.knodel@ndsu.edu

 

READY FOR TOMATOES

Being new to North Dakota (relatively speaking) and the Red River Valley, well, that means I have a lot to learn. Particularly when it comes to successfully growing tomatoes.

Every year, starting sometime in early April, I start to get anxious to plant my tomatoes. Never mind the warnings by more seasoned growers in the area, who encourage me to "be patient." And, they add, "You’ll be sorry if you try to plant too early." Anyway, probably for the best, Nature has not cooperated with my burning desire to plant early for the past 3 years – it has delayed my planting to the second or third week of May. Since I consider myself a ‘lazy gardener’ (I’m not one to use soil-warming techniques such as plastic mulch or plant protectors such as ‘water wall’ style devices. Since I don’t stake my tomatoes, my tomatoes would really be set back if I planted them too early. Tomatoes are sensitive to chilling – fruit set and yield can be dramatically reduced by cold temperatures earlier in the growing season.

So, with a shorter, cooler growing season, I wondered which tomatoes would perform well in the Red River Valley. I turned to some ‘locals’ and asked them their advice about tomato varieties: "Since I’m a ‘lazy gardener’ and don’t plan to do anything special to warm up the soil, which varieties do you recommend?" I asked a few die-hard gardeners. My informal survey of small sample size resulted in two variety suggestions that consistently came up: Sheyenne and Cannonball. These varieties, developed by NDSU Professor Emeritus Dr. Neal Holland, were released in the ‘60s and ‘70s. They are still available in select local nurseries. I tried the Cannonball tomato last summer, after a friend brought a few in to campus for taste-testing. It rivaled my favorite heirloom variety in flavor and exceeded my favorite heirloom in its consistent smooth shape and good size (not overly big; medium size to large plum). It was just right for slicing in a salad or eating right out of hand. Sheyenne, I hope, will be just as tasty. Both varieties and other popular hybrids will be in my garden this year.

Some hybrid tomatoes also appear to perform favorably, according to annual tomato variety trials performed from 1996-2000 at Oakes Irrigation Research Site (NDSU Carrington Research Extension Center) by Richard Greenland, Leonard Besemann and Heidi Eslinger. You can view these results and other variety trial results by going to the following website: http://www.ag.ndsu.nodak.edu/oakes/varpt.htm

Kasia Kinzer
NDSU Plant Diagnostic Lab
diaglab@ndsuext.nodak.edu
701-231-7854
206 Waldron Hall, PO Box 5012
Fargo, North Dakota 58105
http://www.ag.ndsu.nodak.edu/diaglab


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