NDSU Crop and Pest Report

FROM AROUND THE STATE


ISSUE 10  July 3, 2003

GRASSHOPPERS CONTINUE TO BE A PROBLEM

Second to fifth instars can be found in fields. Young grasshoppers take about 7-10 days to develop from one instar (growth stage) to the next. After the 5th or 6th instars, they mature into adult grasshoppers, usually mid-summer. It is important to continue monitoring field edges and fields, since young grasshoppers become more mobile as they mature.

SUNFLOWERS:

SPOTTED SUNFLOWER STEM WEEVIL Have Emerged over the past weekend in cages with infested sunflower stems at the North Central Research and Extension Center in Minot. Adult sunflower stem weevils are about 3/16 inch (4 to 5 mm) long and grayish-brown with varying-shaped white spots on the wing covers and thorax. The snout, eyes, and antennae are black. The snout is narrow and protrudes down and backward from the head. Damage by larvae of sunflower stem weevil causes serious stalk breakage when larval populations are large. The economic threshold is one adult per 3 plants. Some high populations of 2 stem weevils per plant have been reported in South West Region and spraying is underway.

BLACK SUNFLOWER STEM WEEVIL is also present in sunflower fields. Adults are 3/32 inch (2.5 mm) long from the tip of the snout to the tip of the abdomen. The snout is very narrow and protrudes forward from the head, which is smaller than the large, oval-shaped body. Damage from the black stem weevil has not been well documented, but severe pitting on the cotyledons or seedling sunflowers by adult feeding has caused some fields to be sprayed this year in the South West Region. However, in most cases populations are too low to cause economic damage to sunflower. Stalk tunneling causes only minor injury to the plant.

SUNFLOWER BEETLE continues to be a problem in localized areas of North Central Region. Adults, eggs, and larvae can be found in fields now. Timing of insecticide sprays is the issue, since most adults are near the end of their reproductive egg-laying period. Many producers may now want to wait for eggs to hatch into larvae in about a week. Larvae feed for about six weeks.

ALFALFA:

ALFALFA WEEVIL LARVAE ARE NUMEROUS in alfalfa field now. Larvae need about 3 weeks or more to develop into pupae (cocoons). Field damage have been observed over the economic threshold of 30% of the stem damaged. Fortunately, most fields will be cut soon as a control measure. It is interesting to note that after swathing, larvae are feeding beyond the swath row (perhaps, due to the high populations). Typically, larvae will feed primarily underneath the swath.

ASH-GRAY BLISTER BEETLES were also reported in alfalfa. Blister beetles produce a toxic substance called cantharidin. Livestock come in contact with blister beetles when they consume infested alfalfa hay. Horses are most susceptible to the toxin, while sheep and cattle are more tolerant. For example, a few blister beetles can cause colic in horses. Be sure to check hay for blister beetles prior to cutting. Blister beetles are gregarious and are often found in high numbers in localized areas of the field. If so, delay harvest for a few days since blister beetles may move out. If blister beetle persist in the field, an insecticide labeled for alfalfa forage will control beetles. Dead beetles will most likely fall to the ground and should not be picked up by the harvesting equipment. Observe label rates, pre-harvest intervals, restrictions and avoid treating fields at peak bloom to prevent bee kill.

SMALL GRAINS:

APHID POPULATIONS ARE INCREASING in the North Central region. Any late planted fields will be attractive to aphids. Aphids vector barley yellow dwarf virus, which can be devastating if the crop is infected prior to heading. An economic threshold is when 85% of the stems have one or more aphids.

WHEAT MIDGE degree days are moving along fast with the hot summer days! Most of the North Central and Northwest Regions are between 1300 to1500 degree days when the female wheat midge emerges. The female emerges at 1300 degree days and emergence is 90% complete at 1600 degree days (degree day base = 40 degrees F). It is always a good idea to scout any wheat/durum fields in the susceptible crop stage – heading to early flowering during female wheat midge emergence. Scouting should be conducted at night (after 9:00 PM), warm night temperatures >60 degrees F, and light winds <5 mph. Economic thresholds are one wheat per 4-5 head for wheat and one wheat midge per 7-8 heads for durum. No field reports available.

High populations of BARLEY THRIPS in barley has been observed in McHenry County ®. Dugan-Dibble). Adult barley thrips are small about 2 mm long and dark brown to blackish with fringed wings. The wingless, immature forms are pale greenish-yellow and blend in with the host making them difficult to see. Thrips feed within the leaf sheath or within the barley head. Damage is cause from the piercing and sucking mouthparts causing leaf tissues to appear white. Losses are generally confined to a reduction in test weight and an increase in small, thin kernels. An insecticide treatment should be applied as the heads emerge from the boot. In this case, the field was going to be sprayed for aphids, grasshopppers, and leaf diseases as well.

SHELTERBELTS / YARDS – SPRUCES

Yellow-headed Spruce Sawflies are causing problems in shelterbelts throughout the North Central and Northwest Regions. Full-grown sawfly larvae are approximately 3/4 of an inch long, olive green with 6 grayish stripes along the body, and have a reddish-brown head. The damage to spruce trees caused by the sawfly can be substantial. Repeated defoliation causes reduced growth and at times tree mortality. Small and medium sized spruces growing in full sunlight appear to be more susceptible (i.e., windbreaks). Spruces utilize significant energy reserves for shoot elongation. Loss of these shoots due to defoliation substantially weakens the tree. This stress may exacerbate other insect and disease problems. Although there are many natural enemies, spraying is often necessary to rescue the tree. It appears that spraying during early larval stages may be the best means of control. (Source: Michael Kangas)

Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center

 

South-Central ND

During the past week (June 25 to July 1), area rainfall ranged from 0 (Streeter) to 1.06 inches (Pillsbury) in the region as recorded at NDAWN (North Dakota Agricultural Weather Network) sites. Topsoil and subsoil moisture generally continue to be adequate. The region’s estimated crop daily water use on July 1: wheat (May 1 emergence) = 0.31-0.38 inches; corn (May 15 emergence) = 0.26-0.32 inches; soybean (May 22 emergence) = 0.22-0.28 inches; and sunflower (June 5 emergence) = 0.23-0.29 inches. Water use data is available at the following NDAWN website:

http://ndawn.ndsu.nodak.edu/index.html.

Wheat and barley growers are strongly encouraged to continue monitoring their late-planted crops that are in the flag-leaf to early-heading stages for leaf disease and to consider fungicide application for control of foliar and head (scab) disease. Refer to the NDSU wheat disease forecasting system for additional information:

http://www.ag.ndsu.nodak.edu/cropdisease/cropdisease.htm

The forecasting system for flowering wheat at Carrington on July 1 indicated: scab spores were low on June 27 and 30 but high on June 25, scab risk was 12% on June 30; During June 24-30, tan spot infection was likely 7 of 7 days, Septoria blotch 4 of 7 days, and leaf rust 1 of 7 days. Also, sclerotina risk for flowering canola was moderate to high in the region on June 29.

 http://www.ag.ndsu.nodak.edu/aginfo/sclerotinia/sclerotinia.htm

Barley yellow dwarf virus has been found in Logan County. Late-planted barley and wheat should be closely monitored for the presence of small grain aphids until the crops reach the heading stage. Grasshoppers are common in the region and leafhoppers can be found. Orange wheat blossom midge has been reported in Burleigh and Wells counties.

The recent warmer temperatures and sunshine have promoted rapid corn and late-season crop growth. Growers continue herbicide application in beans and sunflower. Haying continues between rain events. Some crop planting is still occurring!

Greg Endres
Area Extension Specialist/Cropping Systems
Carrington Research and Extension Center

 

Southwest ND

The first half of June was on target for normal precipitation but at many locations the last half of June was drier than Normal. At Dickinson we received about 70% of normal June precipitation while Hettinger received about 45% of their normal June precipitation. This is in contrast to May where Hettinger received normal precipitation while Dickinson received 110%. Rainfall during June was more variable and localized than in May. Some areas have adequate moisture while other areas are showing moisture stress. Moisture stress has been accentuated by high winds and very warm temperatures causing damage to the crop such as aborted kernels. Crops that were in very good condition two weeks ago with yield potentials have a yield potential of 30 bushels and if rain is not received shortly yields will be lower. In other areas where subsoil moisture is still adequate or where rainfall has been better than average, for example Beach with 3.67 inches of rain for the month of June the crop is looking very good.

Hay harvest progressed rapidly through the later half of June. Alfalfa weevils were noted at many locations so producers should scout for larva feeding on new growth issuing from alfalfa crowns while the hay is still in the swath. If weevil larva numbers are at or exceed threshold levels, spraying is suggested.

Sunflower and corn crops are developing rapidly even in the water stressed areas but these crops will need rain soon if these crops are to continue normal development. Normal July rainfall at Hettinger is 2.10 inches and at Dickinson 2.22. In areas where little stored soil water remains higher than normal rainfall will be needed to carry sunflower and corn crops to maturity.

This past week the southwest IPM scouts found leaf rust, strip rust, loose smut among other diseases in wheat and barley fields.

The Hettinger Research Extension Center Field Day is July 8 and the Dickinson Research Extension Center Field Day is July 9. A Malting Barley Management Tour has been scheduled for the afternoon of the Dickinson Research Extension Center Field Day. This tour will leave at 1 PM and participants will have the opportunity to learn about dryland malting barley production practices and research conducted by the NDSU Experiment Station to improve malting barley varieties and management practices. Details can be found on the DREC web site or by calling me at (701) 483-2349.

Roger Ashley
Area Extension Specialist - Cropping Systems
rashley@ndsuext.nodak.edu


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