Orange Wheat Blossom Midge -- The Basics

Biology

Adult wheat midge are small, orange flies, about half the size of a mosquito. They have overwintered in the soil of infested wheat fields from last year. The adults emerge from the soil beginning in late June and early July. Peak activity, and the greatest risk of infestation, is expected during early to mid July. Egg laying takes place after 8:30 p.m. when the air temperature is greater than 60°F and the wind speed is less than 6 mph. Eggs are laid on wheat heads around and on the florets. Eggs hatch in 4 to 7 days. Larvae are orange colored. They feed on the developing kernels within the glume. No changes in external appearance of the wheat plant takes place. Larvae feed for about 2 to 3 weeks and grow to 1/8 to 1/4 inch long. They drop from the wheat heads in August after rain or heavy dew. WHEAT IS THE MOST IMPORTANT HOST PLANT. Barley is NOT very susceptible to wheat midge.

Action Threshold -- Deciding to treat

Wheat is ONLY susceptible to midge attack between heading and flowering.

The decision to treat wheat for midge should be determined by growth stage and the number of midge found on wheat heads during the evening scouting activities. The action threshold is 1 adult midge per 4 to 5 wheat heads inspected (primary heads and first tillers). At this level of infestation, yield reductions are estimated to be 15%.

How to Scout for Wheat Midge

Monitor wheat fields between heading and flowering. Field scouting must be in the evening from 9:00 pm until midnight. Wind speeds should be below 6 mph and temperatures above 59°F. Wheat midge ADULTS can be seen laying eggs on the wheat heads. Monitor from HEAD EMERGENCE until 80% of the heads have ANTHERS VISIBLE. When anthers are visible, a wheat head is flowering. Visit 3 or 4 different sites in the field. At each location, count the number of midge on several sets of wheat heads (4 to 5 heads per set). Record and calculate your average for the field.

Detecting Wheat Midge -- Other Methods

Scouting is the only recognized way of arriving at an accurate decision to treat a field. There are other methods that may be used to detect the presence of midge in a field for the purpose of recognizing adult wheat midge. None of these methods are reliable for making treatment decisions.

Emergence traps -- a container placed on the soil surface to collect midge as they emerge from the soil. Aids in recognition of midge and alerting a person to the start of emergence.

Sticky traps -- white traps, coated with oil, placed at the same height as the wheat plants and lower in the canopy. Midge adults become stuck to the traps. Aids in recognition of midge and alerting a person to the presence of midge.

Pie tins, paper plates, etc. -- these have been used to quickly collect adult midge in fields for aid in recognition of the insect. Apply cooking oil to the surface of the object and sweep it through the canopy of the wheat plants. Midge and other insects should stick to the surface for easier identification.

Insecticides for Wheat Midge

The only registered product in North Dakota with wheat midge on the label is Lorsban 4E-SG at a rate of 1 pint per acre. Ground or aerial application can provide effective control when timed properly.

AERIAL -- apply in a minimum of 2 gallons of water per acre. Applications should be made in the late afternoon or early evening for best results.

GROUND -- apply in a minimum of 10 gallons of water per acre, using 40 to 45 PSI. Angle nozzles forward at a 45° angle. Applications throughout the evening should be effective.

TANK MIXING -- Lorsban 4E-SG can be mixed with most fungicides. Avoid tin, copper, and zinc materials when mixed for greater than 12 hours. Do Not Apply with Supertin.

Timing Treatments

Timing a treatment is critical for getting the best results. Apply insecticides before 9 a.m. in the morning, or after 6:30 p.m. in the evening, and when the crop is heading to flowering.

If the action threshold is reached, then consider the following:

• if 30% heading, wait up to 4 days then treat with Lorsban 4E-SG;
• if 70% heading to flowering, optimum control should be achieved;
• if 30 to 60% of the heads are flowering (at least one anther visible), spray immediately, but control is likely to be reduced;
• if 80% of the heads are flowering, treatments are not recommended. Applications at this time are no longer effective because larval will already be feeding on kernels and well protected inside the glume OR the plants are no longer as attractive to adult midge and further infestation of primary heads and first tillers is unlikely.

(Submitted by Phillip Glogoza, Extension Entomologist)

Disease Control

Crisis Exemption/Section 18 for Seed Treatment of Sunflower with Topsin M

A crisis exemption was declared effective April 28 for the use of LSP as a seed treatment on lentil. The crisis exemption was followed by a section 18. The exemption was to treat lentil seed for control of seed borne Ascochyta.

The North Dakota State Seed Department tested 8 lots of lentil seed this year. Infection levels ranged from 0.2% to 10.6%, with an average of 2.0%. Levels below 10% may be of little significance in a dry year, yet levels of 1% or less could cause substantial damage in wet years; most samples had levels this high or higher.

A crisis exemption was declared on May 2, 1997 for the use of Maxim as a seed piece treatment on potato. The crisis exemption was followed by a section 18. The exemption was to treat potato seed pieces for control of silver scurf. This is a disease that has become much more important since the silver scurf pathogen developed resistance to the benzimidazole fungicides TBZ (Mertect) and Topsin M.

Maxim is to be used as an integral part of a potato disease management strategy. This strategy includes the use of high quality seed pieces and the incorporation of cultural techniques such as: crop rotation and optimal harvest time for tubers to minimize disease development; proper handling of tubers to avoid unnecessary bruising, management and sanitation of equipment and storage areas to reduce inoculum including avoidance of storage conditions that lead to free moisture or condensation; and application of the seed protectant to clean seed pieces with a properly calibrated application system.

On May 2, 1997 the Environmental Protection Agency granted a section 18 for the use of Acrobat MZ (9% dimethomorph + 60% mancozeb), Curzate M-8 (8% cymoxanil + 64% mancozeb), Manex C-8 (8% cymoxanil + 64% mancozeb) and Tattoo C (30.5% propamocarb + 30.5% chlorothalonil) on potato for control of late blight.

Acrobat MZ may be applied by ground or air at a rate of 2.25 lb/A up to a maximum of 5 times per season. There is a 14 day PHI.

Curzate M-8 may be applied by ground or air at a rate of 1.25-1.5 lb/A up to a maximum of 7 times per season. There is a 14 day PHI.

Manex C-8 may be applied by ground or air at a rate of 1.5 lb/A up to a maximum of 7 times per season. There is a supplemental label that permits chemigation. There is a 14 day PHI.

The maximum amount of EBDC (mancozeb, maneb, metiram) fungicide permitted for potatoes is 11.2 lb a.i. per acre. Thus the total amount of EBDC applied per season from use of any product or combination of products may not exceed 11.2 lb a.i. EBDC. If the maximum number of applications of Acrobat MZ are made per season, a maximum of 6.75 lb. of mancozeb will be used. If the maximum number of applications of Curzate M-8 or Manex C-8 are made per season, a maximum of 6.7 lb. of mancozeb will be used.

Tattoo C may be applied by chemigation, ground or air at a rate of 2.3 pt/A up to a maximum of 5 times per season. There is a 14 day PHI.

The maximum amount of chlorothalonil permitted for potatoes is 12 lb. a.i. per season. Thus the total amount of chlorothalonil applied per season from use of any product or combination of products may not exceed 12 lb. If the maximum applications of Tattoo C are made per season, a maximum of 4.5 lb chlorothalonil will be used.

Uptake and Translocation. All four products are systemic. Acrobat, Curzate and Manex C-8 are locally systemic: they are taken up by the leaf and move within the leaf, but do not move into other parts of the plant. Tattoo is taken up by the leaf and can be translocated upward in the plant in the water-conducting tissues. Acrobat requires 2-3 hours for uptake, Curzate and Manex C-8 require 1 hr. and Tattoo requires ½ hr. Acrobat has some antisporulant activity. Curzate and Manex C-8 have 2 days of post-infection (curative) activity and persist 2 days after infection. If the pH of the spray water is above 7 (common in our area), the spray water should be adjusted to pH 5.5 to 6.5 to avoid breakdown of the cymoxanil. Tattoo has antisporulant activity, and is translocated upward into new foliage.

None of these products is translocated downward to provide protection of the tubers.

The following table summarizes some of the above data.

--------------------------------------------------
			    Curzate M-8 
				 or	
		Acrobat MZ   Manex C-8	 Tattoo C
--------------------------------------------------
Label rate	 2¼ lb/A     1.5 lb/A	 2.3 pt/A

PHI		 14 days      14 days     14 days

Maximum no. of 
applications	    5		 7	     5
	
Uptake time	  2-3 hr       1 hr	   1/2 hr
	
Antisporulant 
activity	   Some		--	    Yes
	
Post-infection 
activity	    No	       2 days	     No
	
Translocated 
into new 
foliage		    No		 No	    Yes
--------------------------------------------------

Section 18 Granted for Tilt on Dry Bean

On June 4 the Environmental Protection Agency (EPA) granted a Specific Exemption (section 18) for the use of Tilt on dry edible beans for the control of rust. The section 18 is effective from June 20 to August 31. Tilt is to be applied by ground or air at the rate of 4 fl oz of product per acre. A maximum of 3 applications is allowed. A 28-day preharvest interval and a 7-day grazing or forage feeding interval must be observed. Precautions should be taken to prevent introduction of Tilt laden sediments into aquatic habitats to decrease the likelihood of long term chronic effects on surrounding fisheries resources. Adequate measures should be taken to avoid spray drift and runoff.

Chlorothalonil (Bravo, Echo, Ensign, Evade and Terranil) and maneb are highly effective protectants. As protectants they act only to prevent infection, but do not cure infections. Early in the season growers should apply a fungicide as soon as 2 pustules are found per leaf or there are a couple of "hot spots" in the field. Growers should keep informed of the presence of rust in their area. If rust is present in an area, susceptible varieties should be sprayed before they are bombarded with large spore releases from other fields. It takes about 10 days for rust pustules to develop once infection occurs; spraying after infection has occurred will not prevent these infections from continuing to develop.

Tilt (propiconazole) also can be used under a section 18 (see above). It is locally systemic, provides protection for 14 days and has up to four days of post-infection activity. This provides a little greater flexibility than with the protectant products listed above. However, if Tilt is applied a few days before pustules form, it is too late to stop the infection and pustules will form in spite of the application of Tilt. Thus, the most effective way to use Tilt is as if it were a protectant.

North Dakota and Minnesota Departments of Agriculture received word from the EPA on June 26, 1997 that a Specific Exemption has been granted for 1997 for the use of Folicur (tebuconazole) fungicide on barley for suppression of Fusarium head scab. The conditions and restrictions for this use include: Folicur 3.6 F may be applied once at the rate of 4 fl. oz product/acre, via air in minimum of 5 gallons of water or via ground in minimum of 10 gallons of water. The Sect. 18 label states that Folicur may be applied up to the 50% heading stage, and that Folicur should not be tank mixed with other sterol inhibiting fungicides. This exemption was granted for 150,000 acres of barley in MN and for 220,000 acres of barley in ND. The Specific Exemption does NOT include the use of Folicur on wheat. EPA stated that the research data did not indicate Folicur was significantly better than Benlate or Benlate plus mancozeb in controlling head scab on wheat. Benlate is registered for wheat, but not for barley. Therefore, the Sect. 18 provides barley producers another product, in addition to mancozebs, for heading application.

(Source: Extension Plant Pathologists Roger Jones, Univ. of Minnesota, and Marcia McMullen, North Dakota State Univ.)