Pest & Crop Newsletter
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Corn Borer Season Begins– (John Obermeyer and Larry Bledsoe)
It’s hard to imagine, but it is corn borer scouting time! Although, if the low black light trap catches of moths are an indicator of the larval infestations, then most cornfields will have little damage. Corn throughout Indiana that was planted early and are “tall” compared to surrounding corn may be acting as a “trap crop” and should be scouted for larval damage, “shot-hole” feeding. Corn planted in early to mid May will have less risk of infestation. Typically, corn borers are not able to establish very well on corn less than 18” extended leaf height; this is mainly due to DIMBOA, a plant aglucone, which acts as a “built-in insecticide.” Thus, emerging larvae may not survive once they begin to feed. If an impregnated female is not able to find a suitable corn field to lay her eggs, she has hundreds of other hosts (i.e., soybeans, potatoes, grass weeds, broadleaf weeds, flowers, etc.) to choose among. Presently we are conducting a greenhouse experiment with Bill Johnson, Purdue Extension Weed Scientist. We have been infesting giant ragweed seedlings with newly hatched European corn borer and have found that many plants were infested and killed. Perhaps with this season's slow growing corn crop, corn borers will control the ragweeds that escaped the herbicides! Go to http://www.entm.purdue.edu/entomology/ext/fieldcropsipm/b/ECB.HTM for detailed management guidelines. More on this pest later.
Potato Leafhopper Sampling Should Begin Soon– (John Obermeyer and Larry Bledsoe)
Potato leafhoppers are small, wedge-shaped, yellowish-green insects that remove plant sap with their piercing-sucking mouth parts. Leafhopper feeding will often cause the characteristic wedge-shaped yellow area at the leaf tip, which is referred to as “hopper burn.” Widespread feeding damage can cause a field to appear yellow throughout. Leafhopper damage reduces yield and forage quality through a loss of protein. If left uncontrolled for several cuttings, potato leafhoppers can also significantly reduce stands.
Potato leafhopper damage can be minimized by spraying alfalfa with an insecticide or by planting resistant varieties. It is critical to note, however, that insecticide treatment is preventative rather than curative. Thus, to effectively prevent economic losses, treatments must be applied before yellowing occurs. Usually the best results are obtained when treating small alfalfa, so be sure to watch the alfalfa for leafhoppers after cutting. The need to treat for leafhoppers can be determined prior to the appearance of damage if fields are surveyed on a regular basis. To assess leafhopper populations and the potential for damage, take at least 5 sets of 20 sweeps with a 15" diameter sweep net in representative areas of a field. Carefully examine the contents of the sweep net, count the number of adults and nymphs, and calculate the number of leafhoppers per sweep. Use the guidelines given below to determine the need for treatment. For recommended insecticides see Extension Publication E-220, Alfalfa Insect Control Recommendations - 2003 (Revised 5/2003) which can be viewed at http://www.entm.purdue.edu/entomology/ext/targets/e-series/e-list.htm.
Prepare Grain Bins for Wheat– (John Obermeyer and Larry Bledsoe)
Harvest time for the 2003 wheat crop will soon be here. Preparing bins for storage now goes a long way toward preventing insect infestations during the summer. Several species of insects may infest grain in storage. The principal insects that cause damage are the adult and larval stages of beetles, and the larval stage of moths. Damage by these insects includes reducing grain weight and nutritional value; causing contamination (alive or dead); odor, mold, and heat damage problems that reduce the quality of the grain. Newly harvested wheat may become infested with insects when it comes in contact with previously infested grain in combines, truck beds, wagons, other grain-handling equipment, augers, bucket lifts, grain dumps, or grain already in the bin. Insects may also crawl or fly into grain bins from nearby accumulations of old contaminated grain, livestock feeds, bags, litter, or any other cereal products. Insect infestations can be prevented with good management practices. Now that many grain bins are empty, the following guidelines should be used before the 2003 grain is placed in bins:
Click for Table
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Stalk Borer– (Ron Blackwell)
Click Beetles– (Ron Blackwell)
Rootworms– (Ron Blackwell)
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Can Postemergence Callisto Activity on Grass Weeds be Improved with Atrazine?- (Earl Creech and Bill Johnson)
Callisto (mesotrione) is a relatively new herbicide with activity on a number of both grass and broadleaf species. Callisto is labeled to be preemergence (PRE) or postemergence (POST) applied in corn and inhibits HPPD, a blockage which leads to bleaching symptoms in susceptible plants. A number of researchers have observed that the efficacy of Callisto + atrazine is substantially more than Callisto alone, particularly on grass weed species and certain broadleaves such as giant ragweed. Greenhouse work has recently been completed at Utah State University to examine this potential interaction and was supported by observations in the field. Photosynthesis and growth of four weed species (green foxtail, barnyardgrass, velvetleaf, and redroot pigweed) following foliar applications with either Callisto (3 oz/A), atrazine (1 pt/A), or a tank mix of Callisto (3 oz/A) + atrazine (1 pt/A) were compared in a greenhouse experiment (Figure). Photosynthesis and dry mass of barnyardgrass, redroot pigweed, and velvetleaf were significantly reduced by Callisto and atrazine alone and in combination. Long-term photosynthesis and dry mass of green foxtail plants were not suppressed by either herbicide applied alone, but plants treated with the Callisto/atrazine tank mix did not regain photosynthetic capacity and had significantly lower dry mass. Shoot dry mass of broadleaf weeds was reduced by all three herbicide treatments, except large redroot pigweed plants treated with mesotrione alone. In the field, POST Callisto controlled redroot pigweed and velvetleaf but failed to adequately control green foxtail. Tank mixed applications of Callisto and atrazine resulted in a 3-fold increase in green foxtail control (64%) and more consistent control of redroot pigweed over Callisto alone. In conclusion, tank mixing Callisto and atrazine POST:
Herbicide-Related Corn Injury Reports- (Bill Johnson, Glenn Nice and Tom Bauman)
We have received a number of herbicide injury reports during the past 2 weeks. In most cases, the cause of the injury is related to stressful weather conditions which have reduced the plant’s ability to metabolize or degrade the herbicide. In some cases, because corn was planted at such a rapid rate in late April and early May before rainy weather set in, growers and custom applicators were not able to spray soil-applied herbicides before the crop emerged. As a result, many soil-applied products were put on emerged corn. This resulted in the corn plant receiving a much higher dose of herbicide than if the products were applied to the soil, and diluted before being absorbed by the corn plant. The following is a summary of the most common injury cases observed thus far. Atrazine/chloroacetamide injury. A few cases of this type injury have been observed when the products were applied to emerged corn and adjuvants, 2,4-D, simazine (Princep, others) were added to the mixture to control emerged weeds. In other cases the atrazine/chloroacetamide premix was applied in a liquid fertilizer solution to emerged corn. Symptomology observed is short, stunted corn with necrotic tissue on the leaf edges and lower leaves may be burned off. In addition, larger plants will show buggywhipping and twisted whorls that were discussed by Bob Nielsen in another article. Although some stand loss has been observed in certain fields, in most cases the corn will grow out of this injury when warm, sunny days return. Key points for future consideration of this issue:
Lumax/Callisto and Balance Pro injury. Callisto is one of the components in Lumax. We have observed a few cases of bleached corn caused by these products. Injury is typically located in low or wet areas on the field and on sandy soils. Symptomology observed is short, stunted plants with chlorotic tissue on older leaves with new leaves appearing normal in color. Injury is occasionally more severe when these products were applied with higher rates of atrazine (1.5 lb ai/A or more). Injury from these herbicides is typically more noticeable than most other herbicide families. Recovery and yield potential is good if less than 30% of the plant tissue is affected (chlorotic). Key points for future consideration of this issue:
In both cases, corn plants will usually lose one or two of its lower leaves. If one will be using postemergence herbicides in these fields, it is advisable to be sure to correctly estimate the corn growth or “V” stage to avoid more injury problems. Information on staging corn growth is available in past issues of the newsletter and on the “Chat and Chew” website at http://www.agry.purdue.edu/ext/corn/cafe.
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Scab (Fusarium Head Blight) of Wheat- (Gregory Shaner, Andreas Westphal)
A couple of weeks ago an article in Pest & Crop discussed the likelihood of wheat scab in various regions of Indiana. These probabilities were calculated from a weather-based disease forecast. For southern Indiana, the model predicted about a 50:50 chance for a severe epidemic. It looks like the coin landed on the wrong side. While planting soybeans at SEPAC (Jennings County) yesterday (finally!), Shaner saw scab in several wheat fields and plots. Westphal observed scab in wheat at SWPAC, near Vincennes, an area where the disease forecast also predicted about a 50% chance of severe scab. In one bulk field at SEPAC, 12% of the heads had scab. Severity (the amount of scab per head) was low, averaging 1.1 spikelets. At this time, casual inspection of a field may lead to considerable underestimation of the number of diseased heads because it’s easy to overlook a head with only a single blighted spikelet. However, once the fungus has infected a spikelet, it moves into the rachis and then spreads up and down the head from the point of infection. Over the next week or so, depending on temperature, more spikelets on infected heads will become blighted, and so infected heads will become more conspicuous. The wheat at SEPAC is just at the early milk stage of growth (Feekes 11.1), so the potential for damage to the grain is considerable. Scab has been with Indiana growers for a number of years now. Fields following a crop of corn, in particular no-tillage fields, are especially at risk. The fungus that causes scab also causes a stalk rot on corn. The fungus produces spores on the corn debris on top of the soil while the wheat crop develops. During flowering of wheat, the most vulnerable period for scab, spores of the fungus are copious in the field and can infect the wheat crop when conditions for infection are favorable. Recognition of scab may be complicated by the presence of glume blotch (see companion article). This disease causes the tips of glumes and lemmas to turn dark brown. Scab causes a premature bleaching of the head tissue. The entire spikelet, not just the outer glumes, turns white. When weather is humid, a pink growth (spores of the scab fungus) is evident on scabby heads, particularly at the base of the spikelet. With careful examination of heads, it is possible to distinguish these two diseases.
The wet weather that has favored wheat scab has also promoted development of leaf and glume blotch. Leaf blotch is caused by at least two different fungi: Septoria tritici and Stagonospora nodorum. Stagonospora has been the more troublesome of the two for several years in Indiana, and appears to be the main cause of leaf blotch again this year. Infections first appeared early in the spring on lower leaves, but are now showing up on the flag leaf (F) and the leaf below (F-1) and can also infect the wheat head. These plant parts are critical for grain fill, so their premature destruction by leaf and glume blotch results in poorly filled grain, meaning low yield and test weight. In southern Indiana, there are numerous infections on the flag and F-1 leaves. The disease has not progressed quite this far yet on wheat in the central part of the state. The lesions on these upper leaves are still mostly small, brown spots, but they will enlarge to become elliptical spots up to 1/2-inch long. Mature lesions are tan with a dark center. Leaf tissue surrounding the lesion may be yellow. As more infections develop on these upper leaves, individual lesions coalesce to produce large dead areas of irregular shape. The current and predicted cool weather will slow down disease development, but it is also slowing down the development of grain. Where disease has already reached F-1 and F, there is potential for damage. When Stagonospora nodorum infects heads, the disease is called glume blotch. Initial symptoms usually appear on tips of glumes and lemmas. These organs become chocolate-brown. Close examination of these brown areas will reveal small bumps. These are the tips of embedded pycnidia, the fruiting bodies of the fungus. Under wet conditions, spores produced in these pycnidia are released and can cause additional infections on heads and leaves. Growers who applied a fungicide to their fields should check sprayed and unsprayed areas to evaluate the efficacy of treatment in suppressing the disease.
While taking a quick look at a wheat variety trial at SEPAC (Jennings County) on 2 June, Shaner found a focus of stripe rust. There are three rusts that attack wheat: stem rust, leaf rust, and stripe rust. Stripe rust is more commonly found in regions that have mild winters and long, cool springs. In the U.S., it’s mainly a problem in the Pacific Northwest and parts of California. In recent years, it has been showing up frequently in the southeastern U.S., and occasionally in Indiana. Stripe rust has been prevalent this spring in parts of Kansas, Oklahoma, Georgia, and Arkansas. Infections on the wheat at SEPAC were mainly on the upper two leaves (flag and leaf below), suggesting that the first spores of the stripe rust fungus did not arrive until after these leaves had emerged. Southerly winds probably carried spores up from Arkansas and other points south.
Stripe rust differs distinctly from leaf and stem rusts in two ways. The pustules of stripe rust are yellow (the disease is known as yellow rust in many parts of the world), whereas pustules of leaf rust are orange and those of stem rust are brick red. Pustules of stripe rust also develop in long stripes along the leaf veins. Following infection of a leaf by a spore of stripe rust, the fungus produces runner hyphae. These internal strands of the fungus extend for several inches in the leaf and give rise to pustules along their length. The major veins in the wheat leaf restrict the lateral growth of these hyphae, which is why the pustules form narrow stripes. However, if several infections occur on a single leaf, its entire surface may be covered with pustules. Another characteristic of stripe rust is its tendency to develop in foci within a field. This means that there may be a small area (a circle or elliptical area in a field) where plants are severely rusted, with little rust found in other areas in the same field. Unlike other rusts, spores of stripe rust seem to land close to where they were produced, giving rise to isolated “hot spots” (foci) of the disease. When a spore happens to land on a leaf and infect, it will produce new pustules after a few days. These pustules are masses of spores, each capable of causing a new infection. Since the disease is so uncommon in Indiana, wheat breeders in this part of the country are not able to select for resistance to stripe rust, and it is likely that many wheat varieties grown in Indiana are susceptible to stripe rust. Stripe rust has never been a major problem in Indiana. We normally progress from weather that is too cold for the fungus to weather that is too hot in such a short time the disease does not have a chance to become severe. The cool, moist weather of recent days has been ideal for stripe rust, and weather predictions indicate more of the same, so we may see more stripe rust than usual.
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Cold Weather Impacts on the Soybean Plants- (Ellsworth P. Christmas)
A number of individuals have expressed concerns regarding the very slow emergence and growth of soybeans. The name of the game is low temperatures, both of the air and the soil. For the past 14 days, nighttime air temperatures at Wanatah were at or above 50°F for eleven nights. The Agronomy Research Center had ten nights of air temperatures at or above 50°F. Southern Indiana was not much better with low air temperatures at Dubois at or above 50°F six of the past 14 nights. Soil temperatures fared a little better with nighttime lows at or below 60°F about half of the time the past two weeks, but in all cases above 50°F. Mean bare soil temperatures have ranged in the low 60’s to high 50’s over much of the state the past two weeks. Soybean seed will begin the process of germination at soil temperatures of 50°F or above, but the process is very slow. The most rapid emergence occurs at soil temperatures of 70 to 80°F. It is quite typical that at current soil temperatures, three or more weeks may be required for emergence. The major risk of slow emergence at low temperatures is the increased probability of injury to the seedling from fungi and/or insects. Low nighttime air temperatures can cause injury to the soybean plant or can result in very slow vegetative growth. Many times a soybean plant can tolerate temperatures as low as 28°F without injury, but under certain conditions temperatures well above freezing can result in plant injury or death. Cold conditions can result in water stress in the plant and can be one of the causes of low temperature injury to the soybean plant depending on the length of time exposed to the low temperatures and the relative humidity. Research data shows that chilling the soybean plant for one week at temperatures close to the temperatures of the past two weeks can result in reduced leaf elongation, rate of leaf emergence, and CO2 uptake. Usually, all of these will return to normal when temperatures return to levels at or above 75°F. Low soil temperatures also result in a reduction of nodule formation and activity. Soybean plants that had just emerged prior to the cold soil temperatures may exhibit nitrogen deficiencies once air temperatures return to normal and the plants grow rapidly. This is the result of a demand by the plant for nitrogen greater than that available from the cotyledons and the soil. Once soil temperatures warm to a level suitable for nodule activity, the leaves will become a darker green color and the plant will resume normal growth. All of these stresses may result in a plant with lower internodes shorter than normal, hence short plant for their age. Most of the stresses discussed above should not have any long-term effects on the soybean crop with the exception of the fungal disease potential.
Weather-Related Twisted Whorls in Corn- (Bob Nielsen) Most everyone agrees that Indiana weather conditions during the past 30 days or so can only be described as “crappy” for the growth and development of the state’s corn crop. Daily high temperatures have been primarily in the 60’s and low 70’s. Daily low temperatures have been in the 50’s and even 40’s. About the only good news overheard down at the Chat ‘n Chew Café is that surface soil moisture levels have been replenished in most areas of the state, although in many areas rainfall has been excessive. We know that warm, sunny weather will eventually return to the Hoosier state. We also know that corn, being a temperature-dependent crop, will respond to that onset of warm, sunny weather by shifting to a faster rate of development. Therein lies the cause for issuing this fearmonger alert. When periods of slow corn development (typically, cool cloudy weather) are followed by a sharp transition to periods of rapid corn development (typically, warm sunny weather plus ample moisture), scattered plants throughout fields may begin exhibiting unusual symptoms of twisted whorls. The whorls of the affected plants appear tightly twisted, bend over at right angles, and remain unfurled for quite some time.
One’s natural instincts would blame the twisted growth on herbicide injury. Where cell growth inhibitor herbicides are applied pre-plant or pre-emergence, shoot uptake of the herbicide by the emerging seedling can indeed result in twisted growth of the young plants. Late application of growth regulators can also cause twisted whorls in older plants when leaves and whorl intercept a substantial amount of the herbicide. It is important to recognize, though, that twisted whorls of corn may appear in fields where none of this herbicide chemistry has been applied. Some hybrids react to a rapid change from poor to good growing conditions by basically going “bonkers” as their rate of development speeds up. For some reason, the upper whorl of some plants sometimes won’t unfurl properly as if the rolled leaf tissue has lost its elasticity. Younger leaves deeper in the whorl continue to develop rapidly, but are unable to emerge from the tightly wrapped upper leaves. The subsequently tightly twisted whorl then bends and kinks from the pressure exerted from the younger leaves’ continued growth. The growth stage where I’ve observed this phenomenon in past years was around four to six visible leaf collars (somewhat less than knee-high). That growth stage accurately reflects that of early-planted corn right now and, in fact, I’ve received a few reports of the occurrence of the phenomenon from various areas of the state. At the peak of the problem, the appearance of these plants is indeed unsettling and one would think that the whorls would never unfurl properly. Given another week, though, twisted whorls of most of the plants will unfurl and the plants subsequently develop normally. If you didn’t notice the twisted growth to begin with, you may notice the appearance of “yellow tops” across the field after the whorls unfurl. The younger leaves that had been trapped inside the twisted upper leaves emerge fairly yellow due to the fact that they had been shaded for quite some time. In addition to being fairly yellow, the leaves will exhibit a crinkly surface caused by their restricted expansion inside the twisted whorl. Another day or two will green these up and the problem will no longer be visible. The Good News: Yield effects from periods of twisted growth caused by weather-related causes are minimal, if any. For more images of this oddity, see the accompanying image gallery.
More Thoughts on Southern Indiana Delayed Corn Planting- (Bob Nielsen) Increasingly aggravating rainfall throughout southern Indiana continues to interfere with the completion of corn and soybean planting. As of June 1, the Indiana Ag. Statistics Service reported that only 51% of the intended corn acres and 22% of the intended soybean acres had been planted in the southern crop reporting districts of Indiana. Corn growers are particularly frustrated with the delayed planting situation. Last week I indicated that one small bit of good news is that southern Indiana corn growers can avoid drastic changes to hybrid maturities for quite some time due to that area’s longer growing season and corn’s ability to adjust its heat unit requirements with delayed planting (Nielsen, 2003). Listed here again are the safe hybrid maturities for two planting periods:
While a switch to significantly earlier hybrid maturities is not physiologically warranted for a couple more weeks, growers may nonetheless want to consider switching to earlier maturities to reduce their potential grain drying costs in the fall. Long-term plot data from Pioneer Hi-Bred International (Iragavarapu, 2003) indicates that the yield potential for late, medium, and early maturity hybrids becomes very similar as planting is delayed beyond June 10 in the central U.S. Corn Belt. Grain moisture differences at harvest, on the other hand, remain similar among the hybrid maturities, if not more dramatic, as planting is delayed. Final Note of Caution: Growers who elect to switch to earlier maturity hybrids for mid- to late June plantings in southern Indiana must also remember to select hybrids with acceptable disease tolerance because of the greater risk of leaf diseases with late-planted corn (Vincelli, 2003). This is especially true if you are considering maturities unusually early, and therefore agronomically unadapted, for your location. Don’t forget, this and other timely information about corn can be viewed at the Chat ‘n Chew Café on the Web at http://www.kingcorn.org/cafe. For other information about corn, take a look at the Corn Growers’ Guidebook on the Web at http://www.kingcorn.org.
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