June 19, 2003
In this issue
§ Insect update
§ Magnesium deficient corn
§ Presidedress Soil Nitrate Test results
§ Diagnosing plant growth problems
§ Fusarim head blight (scab) of wheat probability for Michigan
§ Stripe rust in wheat
§ Regional reports
§ Weather news
With the cool spring and delayed insect development, alfalfa weevil larvae (some quite small) and potato leafhopper (PLH) are being found together in alfalfa. If a field is still not harvested, then cutting in the next few days will kill many weevils, plus PLH eggs and some nymphs. Watch regrowth for damage from both insects. For weevils, the threshold for treatment is 6 to 8 weevils per square foot, or 25 percent of the new tips with feeding damage. For PLH, the threshold is only 20 insects per 100 sweeps (= 1 PLH in 5 sweeps) in 3-inch alfalfa. Some fields were already harvested a while back, but small weevil larvae are still present. In this case, use the weevil thresholds you would normally use before first cutting; that is 40 percent of the stems with feeding damage. For PLH, the thresholds increase to 50 per 100 sweeps in 3- to 8-inch alfalfa, and 100 per 100 sweeps (= 1 insect per sweep) in 8- to 12-inch alfalfa.
There are numerous insecticides registered for alfalfa that include both weevils and PLH on the label. These include such products as Ambush, Baythroid, Furadan, Imidan, Lannate, Lorsban, Mustang, Pounce and Warrior. While good on PLH, the Dimethoate label indicates only “reduction of alfalfa weevil larvae” and may not be the best choice if trying to optimize weevil control. However, if your major concern is PLH, and small weevils are still present in the field below threshold, Dimethoate will likely provide enough suppression of the weevil population.
To end on a positive note, the timely rainfall and good plant growth we’ve seen this spring helps alfalfa tolerate insect feeding better.
Bean leaf beetle (BLB) adults are really cooking in soybean. These beetles are very distinctive – ranging in color from greenish to yellow to red, with a black triangle behind the head, a black edge around the abdomen, plus 4 black, square spots on the abdomen. Adults overwinter in leaf litter and wooded field margins. In the spring, these adults emerge and eventually move to soybean fields to feed. The adults chew round holes in the leaves. Young soybeans (V1-V2 stage) can tolerate considerable injury – up to 50 percent defoliation – without yield loss. Published thresholds for V2 soybean range up to 6 beetles per plant because soybeans can compensate for early defoliation. Thus treatment is generally not needed at this point in the season, unless defoliation across the entire field is over 50 percent and there are multiple beetles per plant. The main concern with BLB is actually for damage by the summer generation later in the season. At that point, the beetles feed on pods, damaging developing seeds.
Soybean aphid is present in some fields. We estimate 1 in 20 plants in a couple of our fields on the MSU campus have aphids. We have even found isolated plants with up to 50 to 100 aphids, with ants tending and protecting the colony. Some of the aphid colonies are made up of non-winged mothers with babies. This indicates that aphids have been present in the field for 7 to 10 days, and that the beans were colonized just after emergence. There is buckthorn in woodlots around the campus, and this is the likely source of the aphids colonizing the plots. It is too soon to know if predators will clean up these isolated infested plants, or if aphid numbers will increase.
There have been several reports of magnesium (Mg) deficient corn in Southwest Michigan. Magnesium deficiency symptoms often appear early in the growing season in cold wet soils and may disappear as the soil warms and dries. Here’s what to look for if you suspect Mg deficiency: The first symptoms appear as interveinal chlorosis in the older leaves. The leaf margins then become reddish/purple. See Figure 1. However, one should verify whether or not there is adequate soil Mg.
Magnesium deficiency shows up on acidic sandy soils. And large applications of potash can induce the deficiency. If the soil test Mg level is below 75 lb Mg/a or if potassium (K) exceeds Mg as a percent of exchangeable bases, the soil may not be able to supply adequate Mg. A long-term solution on acid soils is to lime the soil using an appropriate amount of dolomitic lime. On non-acidic soils, Mg deficiency may be corrected by broadcasting 50 to 100 lb Mg/a, or banding 10 to 20 lb Mg/a. Acceptable sources of Mg include: magnesium sulfate (Epsom salts), potassium-magnesium sulfate, and finely ground magnesium oxide.
If the deficiency is severe and/or soil Mg levels are low, then foliar applications of Mg at a rate of 1 to 2 lb Mg/a is recommended. This can be achieved using 10 to 20 lb of Epsom salts applied in at least 30 gallons of water.
If you suspect spots of Mg deficiency in a field, take plant samples in the affected and unaffected areas and send them to a lab for analysis, in addition to soil sampling. This can confirm Mg deficiency.
In looking over the results of the Presidedress Soil Nitrate Tests (PSNT) from the MSU Soil & Plant Nutrient (SPN) Lab, the difference between the manured and non-manured fields is very apparent. The average nitrogen credit for samples received from manured fields is 150 lb N/A-2 ft with a range from 70 to 285. For samples from non-manured fields the average N credit is 67 lb N/A-2 ft with a range from 20 to 150. Many cornfields that have received manure have more than adequate available nitrogen to meet the crop’s need. No sidedress nitrogen is needed. In some non-manured fields, more sidedress nitrogen will be needed than is usually applied. In these situations the PSNT will either save money or improve the corn yield.
With recent heavy rains in some areas of Michigan some farmers are asking how much of the preplant incorporated nitrogen is still in the top two feet or potential rooting zone. A soil sample to two feet is the best way to get an answer for this, but not too many people are anxious to pull soil samples two feet deep. A general guide developed by my predecessor indicates that in sandy soils already wetted to field capacity the nitrogen might move 12 inches for each inch of rain received. Under similar moisture conditions in finer textured soils the nitrogen might move 4 inches for each 1 of rain received. Following heavy or continual rainfall events nitrogen loss by denitrification is more likely in fine textured soils than in sandy soils that drain well.
Each year plant growth abnormalities show up in a variety of crops grown on a range of soil types. These might be due to a nutrient deficiency, disease, insects, nematodes, pesticide injury, tillage or some other cause. In diagnosing a plant growth abnormality, first observe the field noting where in the terrain or landscape the problem is located and whether there is a pattern. Observe the plant closely noting the nature or pattern of the abnormality or injury. Look at both the top and bottom sides of the leaves as well as the stem for the presence of injury or insects. Split the stem open to determine whether or not there is any discoloration. Use a spade or shovel to dig up the roots and gently remove the soil. Observe the roots for color and growth habit.
When a nutrient deficiency is suspected, collect plant or leaf tissue samples from the problem area and from a good area in the field. Even though interpretation guidelines exist for “normal” element concentrations in various crops there are variations in varieties. The “good” sample serves as the reference. Also, collect soil samples from the problem and good areas and have them analyzed for available nutrient levels. A quick soil pH measurement can sometimes help determine which elements might or might not be the cause of a deficiency.
The last two years magnesium deficiency has been observed in corn during the early growth. This is more likely to occur on sandy soils, especially if the soil pH is below 6.0. Application of high amounts of potassium might also contribute to magnesium deficiency. Manganese deficiency is frequently observed in soybeans, especially when the soil pH is above 6.5. Boron deficiency is more likely to occur in second or third cutting alfalfa if rainfall and soil moisture is below normal. Observed nutrient deficiencies can be corrected by spraying the appropriate nutrient on the foliage. Suggested rates are 0.5 to 2 lb Mg/A, 0.5 to 2 lb Mn/A and 0.3 lb B/A. A regular soil testing program can help in diagnosing plant growth problems and/or in preventing nutrient deficiencies from developing.
The models predicting the potential for fusarium head blight of wheat can be found by clicking on the link at: www.cips.msu.edu.
Model 2 is the only appropriate model to use at this time. This model predicts a very low probability for head blight to develop in Michigan this year. Generally, temperatures were too low during times when rain or relative humidity was favorable for disease development. The warm weather over the past week has really accelerated wheat growth, and most of the state is past the window when Folicur can be applied.
Stripe rust of wheat is caused by the fungus Puccinia striiformis. Stripe rust is usually a problem in wheat when cool temperatures occur throughout the wheat-growing season. The disease is favored by temperatures in the 50’s and 60’s and is inhibited when there are several days of temperatures in the mid-80’s. Stripe rust was observed in wheat on the MSU campus last week. The overall incidence was low, and severity was low to moderate. Continued development should be slowed or stopped as temperatures in the mid-80’s are expected over the next week.
A good source of information on stripe rust, including
excellent pictures, can be found at:
www.oznet.ksu.edud/path-ext/factSheets/Wheat/Wheat%20Strip%20Rust.asp.
Fungicides are not recommended as the disease is not widespread in Michigan and
as warmer daytime temperatures prevail.
Weather has been mixed, with 2 inches of rain last Thursday (June 12), followed by foggy weather, then clearing, then repeat. At least the temperatures are higher, which is helping growing degree day accumulations.
Alfalfa is getting harvested with the final first cutting finishing up now. Prices started at $2.50 per small square bale. The quality of this first cutting is highly variable. The second crop is off to a nice start however.
Corn is growing nicely with advanced fields at the V6 stage. Sidedressing is going on. European corn borer trap counts at Dundee this week, 147, 87 and 496 for the three traps and 2, 4 and 11 for the traps in southern Wayne County.
Soybeans have not had enough sunlight to do much growing. Bean leaf beetles are feeding and causing some economic damage.
Wheat is finished flowering. Septoria is on the flag leaf, though some fields have very little powdery mildew.
We simply need more sunshine. Fortunately, we have not turned off hot and dry, as in the past two summers however.
We were dry until spotty thunderstorms moved through the area on June 18th. Warmer temperatures have prevailed over the past week with highs in the lower-80’s and lows in the mid-50’s.
In corn, early-planted fields are in the V5 to V6 growth stages. Magnesium deficiency is still prevalent and has produced yellow, stunted plants in the early-planted cornfields. No European corn borer feeding has been detected in our tallest corn.
Early-planted soybeans have reached the V3 growth stage. Later-planted fields have emerged evenly and quickly to produce uniform stands.
Powdery mildew is common in most wheat fields. However, the flag leaves are not severely infected.
Alfalfa harvest is nearly completed. Monitor regrowth for potato leafhoppers.
A week of summer-like weather has improved crop conditions dramatically in the Montcalm area. High temperatures have been in the 80’s five out of the last seven days with mostly clear skies. We did receive a few rain showers late last week but they yielded very little rainfall, just a few hundredths of an inch in most locations. Low soil moisture levels are starting to be of concern in some crops such as second cutting alfalfa and newly planted dry beans. Low soil temperatures have made it up into the 60’s!
The bulk of alfalfa haylage harvest is complete. Fields that were cut early are regrowing nicely with 2 to 6 inches of growth. Alfalfa weevil is present in the Montcalm area. Alfalfa that has not yet been harvested in Newago County is showing extensive damage in some locations. Leafhopper levels are low at this time. Regrowth of alfalfa should be monitored carefully. Harvest of legume grass mixed hay is going full speed ahead as much of this hay is harvested as dry hay.
Early-planted oats are in, or close to being in, boot. Flowering is complete in rye. Wheat for the most part is in good condition at Feeke’s growth stage 10 to 10.5. There is some powdery mildew on flag leaves of susceptible varieties. A low population of cereal leaf beetles have been observed in small grains.
Corn growth stages vary from V1 to V6. This crop has really taken off this week. There is a quite a bit of variability of growth stage and individual plant condition within the field of much of the early planted corn
Sugar beets are growing well. Some spinach leafminer feeding has been observed. Weed control has improved. The most common problems encountered have been herbicide carryover and soil pH issues.
Soybean planting is complete. Soybean growth stages vary from just planted to V3. Dry bean planting is progressing rapidly with 65 percent completed. Most of the rest of this crop will likely be planted this week.
The region benefited from a week of warm dry temperatures. There were light and very scattered showers over the region on Wednesday evening (June 18) that will not keep farmers out of the fields. Windy conditions have caused problems with herbicide applications and there have been reports of drift. One must wait for wind speeds below 5 mph and never spray when winds exceed 10 mph. A wind meter would be an excellent investment to accurately measure wind speed before applications and record keeping requirements.
The largest corn is about V-6 with some later planted fields just emerging. Most of the stands are very good. The near ideal weather over the past week has brought some good color back to many fields. There are still some fields that are yellow and showing signs of magnesium deficiency. Light cutworm pressure has been in a few fields.
Soybeans are progressing rapidly. The early-planted fields have trifoliate leaves. Some of the later planted fields are emerging very quick. Weed pressure is high in many fields and herbicide applications are being made.
Wheat ranges from flowering to just heading. Many fields have powdery mildew and septoria. At this point it has not moved to the flag leaf. Fields should be scouted on a regular basis. Last year several fields were infested with armyworm. None have been seen at this time.
Alfalfa harvest should wrap up this week. This is the first time in a couple of years farmers have been able to make first cutting without it getting rained on because of the nice weather. There are reports of alfalfa weevil on the new growth. Fields should be scouted to determine pest levels. The new seedings look very good.
Dry bean planting should wrap up this week.
Sugar beet fields look very good. Leafminers are present in many fields at low levels. Nitrogen applications are being made.
Sunshine and warm temperatures have been the dominant weather factors this week. Crops are enjoying these conditions with fast growth. European corn borer moth traps have showed very limited flight up to this point.
The first cutting of alfalfa is getting wrapped-up by most growers. Regrowth on early harvested fields looks good due to adequate soil moisture and warm temperatures
Sugar beets are growing very well in this area. Beets in 22-inch rows are covering about 75 percent of soil surface. Spinach leaf miners can be found in most fields but at pretty low levels.
The corn has finally gotten the weather that it has been waiting for. Improved growth and healthy appearance have changed this crop from fair to good this week. Nitrogen sidedressing is going strong in later planted corn, but early corn is pretty well finished.
Most wheat fields are completing flowering this week. Later fields are in early flowering stage. Powdery mildew and Septoria can be found in the lower canopy but most flag leaves are clear of disease. Cereal leaf beetle feeding on the flag leaf is the most prevalent problem with that leaf, but not near a treatment threshold.
Most soybean fields are showing good stands, and later planted soybeans are showing good emergence. Bean leaf beetles have been found in a few fields. The most advanced fields in this area have 3 trifoliates expanded but this sure isn’t the norm.
The few acres of dry beans that are being grown this year were mostly planted this week. Field conditions were good at planting. Early planted beans have had a struggle in the past couple of weeks. They are now emerging but not very vigorous in growth or stand.
Sunny and warm weather the past week has kept fieldwork at peak levels. Temperatures in the 80’s have lasted the past five days, but cooler night temperatures (in the 50’s) still holding on. Soil temperatures are finally creeping up into the 60-70’s. Soil moisture has been excellent for planting and fieldwork.
Corn is really growing now with movement into the V3-4 overall. The warmer temperatures have helped a lot. Most fields have been grassier than normal this year, with a lot of post controls having to be applied this year.
Wheat is at heading in most fields now with some late fields a few days away. Powdery mildew is starting in on the lower canopy of most fields, but not moving up the stem and into the upper leaves yet. Some fields still remaining yellow.
Soybeans are now all emerged and growing well.
Dry beans are still being planted, which is very late for this area. The cooler temperatures and rain a week ago has kept some fields from being planted. Most should be done by the end of this week.
First cutting of alfalfa is well underway with tonnage being down a little from previous years. Most established yields are weedy with grasses and dandelions. No serious pest problems noted or reported yet. New seedings last year look very good.
The weather should be clear through the weekend as dry air moves in behind the front. The next chance of rain is forecast for Monday (June 23).
In the coming week, temperatures should stay warm, dipping a bit on Thursday, but climbing to the upper 70’s and 80’s over the weekend. Low temperatures Thursday and Friday will be in the 40’s. Growing degree day accumulation is still below normal in most parts of the state. In the 6-10 day forecast, above-normal temperatures and above-normal precipitation are expected. The 8-14 day forecast calls for above-normal temperatures and normal precipitation.