North Dakota State University Extension Service - Burke County |
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Burke County AgAlert |
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May 19, 2005 Grass Tetany With the cool weather we’ve had recently and the warmer weather forecast this week those pasture grasses will be growing well. If you have any crested wheatgrass you may be concerned about grass tetany. Grass tetany is a serious, usually fatal metabolic disease of cattle. It most commonly occurs in mature, recently calved nursing cows. Warm, wet weather, rapid grass growth and cold days often leads to grass tetany. Late winter and early spring months are the most common time for grass tetany. Producers should take preventative steps to avoid problems ahead of time. The most common measure is to feed a mineral which is high in magnesium. Loose mineral mixtures are preferred in situations with a history of grass tetany. Provide at least one ounce per day of magnesium oxide to yield 0.6 ounces of magnesium per head per day. This should be started several weeks before calving and continued until the average daily air temp is above 60 degrees (often mid-May). Make sure the form of magnesium in the supplement is either magnesium oxide or magnesium sulfate (not magnesite or dolomitic limestone). Wheat Midge Outlook Good for North Dakota Producers A soil survey conducted last year detected low levels of overwintering wheat midge larvae. This predicts the potential for wheat midge problems and is good news for wheat and durum producers. Wheat midge populations ranged from 0 to less than 500 midge larvae per square meter, with most of the state having less than 200 midge larvae per square meter during 2004. Fields with more than 1,200 midge larvae per square meter are considered high risk. At that point, some control tactic must be used to reduce midge populations. Although a few fields sampled in 2004 had populations close to 1,000 midge larvae per square meter, a tiny, black parasitic wasp kept the wheat midge in check. This wasp, Macroglenes penetrans, parasitizes the larvae of wheat midge and will emerge the following spring and kill the wheat midge larvae. Parasitism can range from 0 percent to 100 percent, with the higher rates occurring in areas where midge populations have been high. With the wheat midge population being low for the last few years, producers unfortunately may see a slow decline in the parasitic wasp population in the future. Weather conditions and the stage of wheat will be important in determining if sporadic outbreaks of wheat midge will cause economic damage this year. Environmental conditions favoring wheat midge development include moist soil conditions prior to emergence in late June to early July, warm, high humidity and light wind conditions during egg laying. Economic injury still can occur if wheat or durum is in the susceptible stage (heading to 50 percent flowering) during wheat midge emergence and egg laying. Damage can reduce crop yields and lower the grade of harvested grains. The wheat midge survey is conducted by the NDSU Extension Service and supported by the North Dakota Wheat Commission. Wheat Midge Degree Days Used as a Guideline for HRSW Risk Assessment Most of North Dakota is now in the high risk planting period, 200-600 Degree Day (DD), for HRSW to wheat midge infestation (see map). HRSW planted during the 200-600 DD period is when wheat is in the susceptible stage, heading, and this timing coincides with peak wheat midge emergence. Prior to 200 DD and after 600 DD, wheat is at less risk to midge infestation due to the period of heading occurring prior to or after peak emergence of wheat midge. Late planted wheat may also be more susceptible to frost injury. The southern tier of North Dakota entered the 200 DD window around mid-April, whereas the northern tier of North Dakota started around May 1st. Outlook for Seed Damaging Insects Favorable Soil temperatures are now above 50ºF in North Dakota, which is the minimum temperature for feeding activity of most seed damaging insects, such as wireworms or seed corn maggots. Unfortunately, the cool weather has delayed crop emergence and this increases the potential for injury from seed damaging insects. These insects cause stand reductions and reduce crop vigor. Producers often first notice the uneven emergence or bare, patchy areas in fields. Dig up the seed and look for tunneling into the seed or seed that is completely hollowed out. Look around soil next to damaged seed for the insect culprit! Remember there are several other factors that can lead to stand reductions: planter malfunction, seedling diseases, and pesticide damage to seed. If fields need to be replanted due to an insect pest, a soil-applied insecticide or seed treatment should be considered depending on the insect present, is the pest still actively feeding, soil temperatures, and plant growth rate. Where wireworms are a problem, a soil insecticide or seed treatment is usually justified, because wireworms continue to actively feed through June. Control of seed corn maggots depends on the soil conditions and crop growth rate. If soil conditions are cool and moist where seed corn maggots are actively feeding, and crop emergence is slow (over a week), an insecticide seed treatment is critical. If soil conditions are warm, and germination / crop growth rate is fast, an insecticide may not be needed for control of seed corn maggots. The growth of crop may be sufficient to protect it from injury. Remember to read the label to be aware of any restrictions as to the amount of product that can be applied per season. Alfalfa Weevil Scouting – Degree Days Update Scouting for alfalfa weevil can be improved by using degree day accumulations to time field visit when weevils are active. Degree days for alfalfa weevil are slowly accumulating; however, we haven’t yet reached the 250-300 Degree Day (DD) mark (base of 48ºF), which is used to initiate alfalfa weevil sampling. Currently, North Dakota is in the low to mid 100’s. Symptoms of weevil injury are small pin-holes in leaves at growing tip in May. This is the best time to begin scouting. Early detection of tip-feeding injury is critical to prevent yield and quality loss when infestation levels are high. Future Crop & Pest Reports will address management decisions and accumulated heat units. Canola: Diamondback moth –The first Diamondback moths were captured in pheromone traps at NCREC, Minot and observed in Fargo around mid-April. This marks an early and the first arrival of these migrating moths into North Dakota from the southern states. Adult moths have also been observed in fields of volunteer canola in southern Manitoba. Fortunately, trap counts numbers are low so far. Crucifer flea beetles – Crucifer flea beetles, Phyllotreta cruciferae, is the main species of flea beetles that attacks canola in North Dakota. It was recently collected on yellow sticky traps at NCREC, Minot. Several people commented on flea beetle activity early in April, but these were other species of flea beetles, such as, the striped flea beetle (Phyllotreta striolata) and the sweetpotato flea beetle (Chaetocnema confinis), which emerge earlier. Warmer weather will trigger higher numbers of crucifer flea beetles in the next few weeks. Cool Weather Slows Degree Day Accumulations for Alfalfa Weevil Degree days for alfalfa weevil continue to slowly climb towards the 250-300 Degree Day (DD) mark (base of 48ºF), which is used to initiate field sampling for alfalfa weevil. Currently, SE North Dakota is the highest with 182 DD accumulated. Further north, DD decrease accordingly with the minimum of 75 DD. The NDAWN website now has a base of 48ºF under Applications and Insect Degree Days, which you can use to access to get the DD accumulations for the state. http://ndawn.ndsu.nodak.edu/insectdd-form.html Time to Scout for Cutworms with Warmer Weather in Upcoming Weeks Watch your fields for any cut plants and dig up any cutworm larvae located under cut plants. The wet soil conditions will cause them to feed close to the soil surface making them easy prey for other predators (sea gulls, ground beetles) and easier to kill with insecticides. Fungal diseases could also cause some mortality with cutworms. The cool conditions will slow their feeding activities and larval development. Since there are early and later season cutworms, activity will continue into late June in ND. The Dingy cutworm, Feltia jaculifera, overwinters as a partially grown larva and is one of the first cutworm species to cause problems during crop emergence from early to mid-May. The moth of the dingy cutworm is known to lay her eggs on sunflower heads from mid-July through September. Crops following sunflowers in rotation are at greatest risk of injury by this cutworm. Other cutworms, the red-backed, Exoa ochregaster, and the darksided, Exoa messoria, overwinter as eggs which hatch in mid to late May. Eggs are laid in the fall and survive in weedy, wet, and reduced tillage areas. Feeding injury by these cutworms normally occurs in late May to early June. Remember, early detection is critical for effective cutworm control, especially in corn, dry beans, sunflowers, soybeans, sugar beets, alfalfa. Cutworm damage is often localized in certain areas of the field, and in some situations insecticide sprays can be targeted at those infested areas. Economic thresholds include: Corn: Begin scouting for cutworms when corn is up to a stand and continue until mid-June. Treat when 3 to 6% of the plants are cut and small larvae (<3/4 inch) are present. Application rate of 15 to 20 gallons of water per acre by ground application is suggested. Dry Bean: Treatment is warranted when one cutworm or more is found per 3 feet of row and the larvae are small (<3/4 inch long). Forage (Alfalfa): Treatments would be justified when more than 2 worms per square foot are present after the hay has been cut - if larvae are not expected to pupate in the next 3 to 4 days. Sugarbeets: Cutworm control in young beets is suggested when 4 to 5% cutting of seedlings observed in fields. A population of 3 to 5 per square foot is recommended in late summer and plant canopy is developed. Soybeans: Economic thresholds for cutworm treatment decisions are not well established. Treatment guidelines used over the years include when one cutworm or more is found per 3 feet of row and the larvae are small (<3/4 inch long). Another guideline is when 20% of plants are cut or when gaps of 1 foot or more exist in the plant row. When making a final decision, consider that surviving soybeans are able to compensate for early stand reductions because of the plants long growth period. Sunflower: Treatment is warranted when one cutworm or more is found per square foot or there is a 25 to 30% stand reduction observed. Please consult the 2005 ND Field Crop Insect Management Guide for insecticide registered for cutworm control in specific crops. http://www.ext.nodak.edu/extpubs/plantsci/pests/e1143w1.htm Efficacy of Seed Treatments against Crucifer Flea Beetles in Early-planted Canola This story is becoming all too familiar. We had similar conditions last year! So far, low levels of crucifer flea beetles have been detected on yellow sticky traps at NCREC in Minot. Higher numbers of flea beetles will begin emerging with warmer weather. There is concern with the early-planted canola and whether the commercially applied insecticide-fungicide seed treatment (Helix xtra, Helix lite and Prosper 400) will still control flea beetles. For any early-planted canola that been in the ground for 21-26 days and barely emerging or in the seedling stage, the residue of the insecticide-fungicide seed treatments will NOT be effective against spring emerging flea beetles! These canola seedlings will be at high risk to flea beetle injury. A foliar insecticide spray will be needed on top of the canola seed treatments as flea beetle feeding activity increases in mid-late May. The economic threshold for flea beetles is 25% foliar damage in seedling canola. Remember, flea beetles can move very fast when weather conditions are warm (>60°F) and quickly defoliate a small canola seedlings when population are high. Registered foliar insecticides for control of flea beetle on canola are: Capture, Decis, Proaxis, and Warrior (pyrethroids) and methyl-parathion (organophosphate). Pyrethroids can be safely tank-mixed with the herbicides labeled in canola. A residual of 7-10 days can be expected from these pyrethroids, only 3-5 days with methyl-parathion. Remember proper timing is very important with foliar sprays! Flea beetle feeding activity usually continues into late June and has peaked during late May to early June the past several years. When the canola plant is 6-8 leaf stage, it can usually out-grow any flea beetle damage and compensate for feeding injury. However, flea beetles can also cause injury to the center growing point and kill the canola seedling under extremely high populations. Research conducted at the NCREC in Minot, Carrington REC, and Langdon REC over the past several years has shown that a seed treatment plus a Capture (1.3 fl oz/acre) foliar spray applied at 21 days after planting has provided the highest and most consistent canola yields over the years (lowest risk level for those risk-averse producers!) compared to seed treatments alone or a single or double application of Capture. This research was conducted under moderate to heavy flea beetle pressures. 2005 Canola Insect Trap Network Pheromone traps are being put out in canola field of the north central and northwest regions of North Dakota for the migratory Diamondback moth, and these traps are useful tools for detecting the flights of the adult diamondback moth. Early trap catches are high >100 moths per trap week in Minot. However, the cold, rainy weather this past week should of cause some mortality with these earlier moths. Weekly trap counts provide good indicators of potential pest problems and the need to scout fields for larvae. Stay tuned for updates as the season progresses. Orbatid Soil Mites – Nuisance for Home Owners If you find many tiny, little black dots, like pepper moving around in your window sills or house siding on warm days, you are not alone. These are microscopic Orbatid soil mites! Orbatid mites can vary in color (see photograph, source: Ray Norton), but they live in the top layer of soil, leaf litter, or other debris. Hundreds of thousands of mites can live in one square meter of soil! The role of Orbatid mites is extremely important in ‘recycling’ nutrients back into the soil. Soil mites are also a food source for other arthropod predators, such as, beetles, ants, larger mites, spiders, and others. Although these mites are sometimes a nuisance in the spring as temperatures warm up, the presence of many mites are a sign of healthy fertile soil. When you are walking on a healthy lawn or field, there are millions of Orbatid mites under your feet! Remember not all outdoor home insecticides will control mites. Desperate home owners can use diazinon or dicofol (kelthane) (not Tempo). Leafy Spurge Hawkmoth, Hyles euphorbiae, flying! The biological control agent, leafy spurge hawkmoth, was observed near Burlington (Ward County) this week, collected by Derrill Fick. This Sphingid moth was introduced and released in the 1980s in North Dakota for control of leafy spurge, Euphorbia escula L. The larvae feed upon the leaves and bracts causing defoliation. By itself, the leafy spurge hawkmoth is ineffective as a biological control agent. Please consult “Moths of North Dakota” NDSU website for pictures of moth and larvae: http://www.ndsu.nodak.edu/ndsu/ndmoths/names/7892.htm Dan Folske |
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