ISSUE 5 June 10, 2010
CONTINUE TO SCOUT FOR CUTWORMS
The early season cutworms (dingy cutworm, pale western cutworm, army cutworm, stripped cutworm) are still active in the Northern tier of North Dakota. Pat Beauzay and I were in the northwest and north central regions of North Dakota on June 7-8 of this week. We found mature dingy cutworm larvae in peas and cereal grains that were at non-economic levels. I also received reports of high populations of cutworms in canola from Renville County and in sunflower in Adams, Barnes and Stutsman Counties. The small (<½ inch), early instars (young caterpillars) of the late season cutworms like red-backed cutworms, darksided cutworm, variegated cutworms and black cutworms can be found now. The bottom line is to continue to be vigilant with cutworm scouting until the end of June. Cool temperatures will delay the cutworm development. Excessive cool, wet soils tend to amplify stand reduction by slowing plant development relative to cutworm feeding. In general, the number of cutworm reports has been lower this year, probably due to soil borne insect pathogens.
For economic thresholds and insecticides registered in North Dakota for cutworm control, consult the 2010 Field Crop Insect Management Guide at:
ALFALFA WEEVILS UPDATE
Growing degree days (base 48 C) for alfalfa weevil indicate that the southeast, east central and southwest regions of North Dakota are at risk for larval feeding activity. Cool weather has slowed development. Again, timely cutting should provide good alfalfa weevil control in first cutting this year!
Figure 1. Alfalfa weevil degree day map (NDAWN, NSDU)
Note: Field scouting for alfalfa weevil is initiated at 300 DD. Major feeding by the alfalfa weevil larvae will occurs from 430 to 595 DD (2nd - 4th instar). At greater than 600 growing degree days feeding normally stops and adult emerge. Please see issue #3 of Crop & Pest Report for scouting and pest management details.
CEREAL APHIDS DETECTED IN SMALL GRAINS
The first reports of migratory cereal aphids (Fig 2) have been reported in the north central, south central and southeast regions of North Dakota. This is early in the season and although there are only low numbers of aphids present, now is the time to get out and scout. Continue scouting until the early flowering. If the weather turns more dry with moderate temperatures (mid-70s F to 80s F), aphid populations can explode quickly and reach economic threshold. To protect small grains from yield loss due to aphid feeding, use either economic threshold:
Figure 2. English grain aphid (P. Beauzay, NDSU)
Cereal aphids transmit a yield robbing disease called barley yellow dwarf virus (see McMullen’s article on page 6). When aphid populations are high, the disease can spread quickly through small grain fields. At greatest risk are later planted fields which attract migrating aphids that are moving from more mature fields.
SCOUT FOR BARLEY THRIPS
Low numbers of barley thrips (1-2 thrips per stem) have been reported in the north central and south central regions of North Dakota (see reports in ‘Around the State’). It seems early for barley thrips with the cool wet June. Typically, hot dry weather conditions favor barley thrips development that may result in crop losses.
Barley thrips are small dark brown to black insects about 1 mm long (Fig. 3). Females have feathery wings while males are wingless. Immature larvae are wingless, pale yellow, white or green with red eyespots. Larvae are difficult to see due to their light, almost transparent color and extremely small size. Adult and immature thrips have a long, narrow body shape.
Figure 3. Barley thrips adult (P. Beauzay, NDSU)
Female thrips overwinter as adults in debris in fields and shelterbelts. Thrips emerge in late May and early June and move into winter wheat/rye and eventually to early seeded barley (preferred host). Occasional, barley thrips will feed on hard red spring wheat and durum as well. There is one generation per year.
Adult and immature thrips cause damage by feeding on succulent plant tissues (puncturing plant cells and sucking out the contents). Feeding injury symptoms are a whitened or bleached appearance (Fig. 4) with gooseneck-shaped stem and heads under severe pressures. Intensive feeding at the beginning of head formation produces small, shriveled grains. Often there is no seed development at the top and bottom of the head (Fig. 3) and intermediate grains are shriveled. When thrips feeding is severe on the flag leaf, kernels do not fill properly and seed weight is reduced.
Figure 4. Barley thrips injury (J. Knodel, NDSU)
Scout for barley thrips from flag leaf to heading. Barley thrips can be found by unrolling the flag leaf away from the stem. Remember, populations will probably be higher at the field edges.
Economic Threshold equals the [Cost of control ÷ Expected value per bushel ($)] ÷ 0.4
Using the cost of control as $8-12/acres (insecticide + application cost) and $3.80/bu of barley (low price range), the economic threshold is 5-8 barley thrips per plant before the crop is fully headed. Using the cost of control as $8-12/acres (insecticide + application cost) and $5.00/bu of barley (high price range), the economic threshold is 4-6 barley thrips per plant before the crop is fully headed.
Once the barley heads the insect damage is done and NO insecticide treatment is advised. The only registered insecticide for barley thrips control in North Dakota is methyl parathion 4 EC at 4-6 fl oz per acre (do not enter treated fields within 48 hours after application). Other insecticides approved for use on barley but do NOT have barley thrips listed on the label include the following active ingredients: beta-cyfluthrin, lambda-cyhalothrin, malathion and methomyl. It is legal to apply an insecticide if it is labeled for use in the crop; however, if the target pest is not listed for that crop, efficacy is not implied by the manufacturer and growers who choose to use the product assume their own liability for any unsatisfactory performance. I did receive some insecticide efficacy reports from 2009 that pyrethroids (beta-cyfluthrin, lambda-cyhalothrin) did work for control of barley thrips, and they are much safer for the applicator.
Although many growers want to wait to tank-mix the insecticide with a fungicide for scab control at Feekes 10.5 (head fully emerged), I do NOT recommend waiting for the optimal timing of a fungicide application for scab control in barley. This is too late for effective barley thrips control and the damage/yield loss is already done by then.
COLORADO POTATO BEETLES ON THE WAY
The first adult Colorado potato beetles of the season were found last week at our field plots near Glynon, MN. Colorado potato beetle is the most common and destructive leaf feeding insect pest of potato in our region. Adults overwinter in shelterbelts and other sheltered areas and emerge from late May through June. Adults (Fig. 5) are about 3/8 inch long with 5 black stripes on each cream-colored wing cover.
Figure 5. Colorado potato beetle adult (P. Beauzay, NDSU)
Adults lay eggs on the undersides of potato leaves. Each egg mass (Fig. 6) contains about 10 to 40 yellowish eggs, which turn orange in color when they are close to hatching.
Figure 6. Colorado potato beetle eggs (P. Beauzay, NDSU)
Early instar larvae are about 1/8 inch long, and are typically found clustered together near the hatching site. Young larvae disperse about the plant and typically feed near the bases of leaves. Late instar larvae (Fig. 7) are about 3/8 inch long and can be found feeding on the leaves anywhere on the plants. All larvae are humpbacked in appearance and orange in color, with two rows of black dots along their sides. Larvae are present from June through July. Mature larvae drop from the plants and pupate in the soil. Second generation adults continue to feed on the leaves before moving into sheltered areas to overwinter.
Figure 7. Colorado potato beetle larva (P. Beauzay, NDSU)
Scouting should begin in late May when adult beetles are first observed. Scout fields thoroughly for egg masses and flag the plants that have them. Be sure to look at the undersides of the leaves! Continue scouting for new egg masses, and observe the flagged plants for egg hatching. Foliar treatments should be initiated at 15 to 30% egg hatching. Depending on the treatment used, a second application may be necessary, so continue scouting for eggs, larvae and adults after foliar treatment.
There are several treatment options available, but great care should be used in developing a chemical management program to prevent the development of resistance in our beetle populations. To aid in developing a chemical management system, we recommend using the IRAC classification system, which is based on insecticide mode of action. For more information about IRAC, go to: www.irac-online.org.
Neonicotinoid seed piece treatments and in-furrow applications are common at-plant strategies. Neonicotinoid insecticides (IRAC Group 4) for seed piece treatments and/or in-furrow applications include Admire Pro, Platinum, Cruiser Maxx Potato, Belay 2.13 SC, Nuprid 2F, and Venom 70 SG. These products typically give excellent control of first generation adults and larvae. However, weather and planting date can influence product efficacy. If neonicotinoid insecticides have been used as seed piece or in-furrow applications, DO NOT use neonicotinoid insecticides for foliar applications if foliar applications become necessary. This practice will speed up the development of Colorado potato beetle resistance to neonicotinoids. Foliar insecticides containing neonicotinoids include Assail 30 SG, Assail 70 WP, Brigadier, Nuprid 1.6F, Provado 1.6F, Leverage, Endigo ZC, Actara, and Voliam Flexi. Also, neonicotinoid seed piece and in-furrow treatments should not be used in consecutive years if fields are adjacent to or closer than ¼ mile from the previous year’s crop.
Growers have several non-neonicotinoid foliar spray options. Coragen (IRAC Group 28) at 5 fl oz/acre has provided excellent season-long control in our trials. A combination of Temprano plus Rimon is also effective. Temprano contains abamectin (IRAC group 6) and Rimon contains novaluron (IRAC Group 15). Chemtura, the manufacturer of Temprano and Rimon, recommends application of Temprano at 8 fl oz/acre plus Rimon at 9 fl oz/acre, followed by Rimon at 2 fl oz/acre 7 to 10 days later. Spinosyns (IRAC Group 5), including Entrust, Success, and Radiant SC are effective, though higher rates and two applications per season may be needed. Pyrethroids have not given good control of Colorado potato beetle in our trials in past years, and we do not recommend using pyrethroids for control of Colorado potato beetle.
For all foliar applications, timing is critical. As always, be sure to read, understand and follow the product labels. Consult your local chemical dealer for current prices.
NDSU Extension Entomology
SUGARBEET ROOT MAGGOT: COOL, RAINY WEATHER DAMPERS ACTIVITY
By now, most adult sugarbeet root maggot (SBRM) flies should have emerged from soil in last-year’s beet fields where they overwintered as larvae. However, the recent cool, windy, and rainy weather in much of the Valley has reduced fly activity levels in recent days.
These weather factors can impact fly activity in two ways. First, they are not conducive to flies taking flight because SBRM flies are not aggressive fliers. As a result of such weather, flies remain in harborage areas such as small grain fields, shelterbelts, and grassy areas like road ditches and field margins. Second, heavy rains that result in long periods of soil saturation can kill the insects as they are pupating (turning into cocoon stage) and emerging as adult flies. Thus, infestations in some areas could have been negatively impacted by rainfall events that occurred during the past week.
As a result of the recent sub-optimal conditions for SBRM flight, fly activity will probably resume at moderate levels when nicer weather returns. Fields should be monitored closely during the next week for a potential resurgence of significant fly activity.
The rainy weather has also complicated postemergence insecticide application efforts for many growers. It is probably too late for additional postemergence insecticide applications at this time in central and southern areas of the Red River Valley.
In the northern 1/3 of the Valley, fields where moderate to high fly activity (exceeding 0.5 flies per plant) has been observed may still benefit from a postemergence application of a liquid insecticide if the application is made by June 14.
If using a chlorpyrifos-based liquid insecticide (Lorsban, Nufos, Warhawk, Whirlwind, etc.), apply it at a minimum of 0.5 lb (a.i.)/acre (1 pint product/ac for most products). Lower rates are not likely to provide sufficient control at this time. Higher rates (up to 1 lb a.i./ac) can provide good control; however, avoid applying the high rate if hot (85 F or warmer) temperatures are expected within a 24-hr period following the application. A light rainfall after the application may improve control because it can help incorporate the insecticide into soil where newly hatched larvae are hatching and beginning to feed. For more guidance on postemergence control strategies, consult the "Insect Control" section of the 2010 Sugarbeet Production Guide or the "Sugarbeet Insects" section of 2010 Field Crop Insect Management Recommendations. Online versions of these publications are located at:
Research & Extension Entomologist