Silking corn received some much needed precipitation over the last forty-eight hours across much of Salem County. On a hot July day, corn in pollination mode can easily uptake .25 to .30 inches of moisture. Depending on the location, some fields only received a day’s worth of rain while other’s under the path of the northeasterly tracking storms received upwards of .80 inches this weekend.

 

Evaluating field water holding capacity. Precipitation is critical to mazimizing grain fill on soils with low water holding capacity under these conditions. Soil compaction in fields that are exhibiting classic surface sealing are exasperating corn moisture stress conditions as seen in this July 23^rd photograph. Combined with the high evapotranspiration rate of the last two weeks, these soils are unable to absorb or retain enough moisture to meet crop removal needs. Now is a good time to evaluate soil water holding capacity and tilth condition and how well the corn hybrid planted on that soil met expectations despite any pressure from silk feeding insects.

When moisture stress occurs makes all the difference. Remember, corn hybrids mature at different times based on their individual need to accumulate heat units. Just before silking is visible, corn plants are in the V12 collar stage. At this stage, one can assume at least 880 heat units since planting at this location. At V12 stage, we can assume the crop emerged 43 to 50 days ago. When fifteen collars are present, the crop is about ten days away from silking. This is when ear size, kernel size and kernel number are determined. Take a moment to look back and see what maturity corn was planted. Do you like what you see? Despite the weather stress? If counting leaves, their should be at least sixteen leaves on the plant before the tassel appears on shorter season hybrids and as many as twenty-one on longer season hybrids.

What happens at silking? Did you know that at silking, 50% of the available nitrogen and phosphorus in the soil is taken up by the crop over the next few weeks. When did you put down nitrogen? Sixty days ago as a plow down but with a delayed planting? Forty days ago at planting? Twenty days ago as a side-dress? Did you split applications?

How many days are left to physiological maturity? An ‘85 day’ corn requires about 2100 heat units since planting to mature. ‘101’ day corn varieties require more than 2400 heat units. It’s the end of July. How many heat units are left in the growing season to reach physiological maturity based on the V stage of the crop? Given the soil moisture holding capacity of the soil, could you have planted that field any earlier? Planted it later? Used a longer or shorter maturing variety? If the planting date had remained the same, would a shorter day or a longer day corn have pollinated better or faired worse given the precipitation pattern at that locale? What if the planting date had been earlier, or later? How did tillage choice impact water holding capacity of that soil?

What next? While a typical field of corn can take up to fourteen days to reach full pollination, some of the crop wil be pollinating every day. This is actually a good thing. Pollen only sheds when anthers are dry and extreme heat can even kill pollen. Corn is wind pollinated. When shed, the pollen clouds will drift from twenty to fifty feet. Last week’s low air quality rating due to the smokey haze over the region was also due in part to the amount of corn pollen in the air locally. Conversely, on overcast rainy days, tassles do not release pollen to the silks below. Too much wind during pollen shed can actually blow the pollen beyond reach.

Lastly, while the silks are being pollinated they have to compete with japanese beetles, corn beetles and a myraid of other silk clipping insects.

If you can tolerate the smell and feel of corn pollen on your eyelashes, put on a rain coat and go for a walk through your crop to see how the interior of the field is fairing this season. Remember as hay comes off and soybeans are sprayed, the bugs are seeking haven in corn.

 

Additional Resources:

Water holding capacity of some NJ soils:

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs141p2_018372.pdf

Crop development:

https://cropwatch.unl.edu/documents/Corn%20Growth%20%20Development%2013-1-1.pdf

 

Crop fields continue to be a smorgesborg for insect and insect vectored pathogens. With four different planting groups of soybean and three of corn, foliar and silk clipping pests are making their presence known in soybeans and corn.

Corn: Japanese beetle feeding continues to expand across soybean fields. The abundance of healthy stands and silk emergence in early planted corn will shift these leaf feeders over to corn silks. This planting group is overall in excellent condition and most fields have obtained maxiumum height and nitrogen utilization. These fields have very high stand populations and leaf development. Hopefully this will help mitigate the edge feeding losses from Japanese beetles and another silk clipper, stinkbugs. In the coming weeks after pollination, good air flow and lower humidity through grain fill is needed to limit mycotoxin development.

Late May and June planted corn up to three feet in height oversaturated just prior to planting continues to show signs of moisture stress, and soil compaction issues. These fields are in the rapid stem elongation phase and were leaf curling this week in the high heat. Several fields are symptomatic for nitrogen deficiency as a result of those earlier ponding events. Soils are sunbaked on the surface and fields with higher clay content are root zone compacted. These are the fields to monitor for economic damage from silk clipping if the crop continues to be under heat stress. To limit further yield losses, these acres are more likely to benefit from insecticide treatments during silking still a few weeks away. Stink bugs in V1 to V6 plantings are most likely to be of economic concern and treatable in this corn group when 1 out of ten plants have bugs; decreasing to 1 out of every four at reproductive stage.

July planted corn is less effected by moisture and heat stress. The root systems of these v1 to v5 plantings have found adequate surface soil moisture from last week’s rains and are loving this heat and humidity. This crop group is highly variable for soil compaction depending on the quality of the soil and the path of heavy rainfall just prior to planting.

Soybeans: Overwintering pests of concern vectoring diseases to soybeans have emerged in abudance from vegetation in field edges, old meadows, and grass hay fields. The acreage and variability in cover crop plantings and cash grain crop plantings last fall was ideal for insect populations and residue infected bacterial innoculums to increase.

Along the south-west side of the county, in uncanopied vegetative beans on sandy soils, wind-rain-sand deposition of soil onto leaves occurred in recent storms and disease progression is evident on stems and leaves. Field comparisions here observed tillage at planting reduced movement of bacterial innoculum onto stems and leaves in canopied stands in contrast to adjacent no-tilled early vegetative stands. On the opposite corner of the county, oversaturated, low-lying loamy fields recently fitted for planting are showing expected variablity in stand establishment.

On better ground without compaction issues, most early planted fields are in good foliage condition.  Early R stage beans that were under heat and moisture stress last week show signs of self-abortion of lower stem flowers. Management of insect feeding and variatal resistance response in these fields is optimum. Crop rotation matched to soil type and timing of inputs stands out as the key niche for uniform early planted stand evaluations. In these ideal stands, evaluate what combination of variety, tillage, prior crop rotation, planting date, and timing of inputs and preciptation thwarted insect vectored diseases.

Observations on later planted beans are quite variable regardless of when inputs were applied. Grasshoppers, japanese beetles, spider mites and thrips have already vectored leaf diseases in this group. Soybean stem borer adults and larva were observed in v4 to v5 fields.

Knowing the weather was just not ideal for this planting group, document signs and progression of insect vectored diseases in the foliage, exterior of stems, interior of stems, cross section of roots, feeder root presence and presence of healthy nitrogen fixing bacteria by variety.

Healthy stems and roots in the vegetative stage are a good sign plants will respond to foliar feeds if needed. Expect insect pressure to continue to build. Soybean diseases overlap as do insect stages and feeding pressure. While one pathogen may be of minimal concern in early planted beans, another may take over second plantings and dominate later plantings as season progresses.

Giant ragweed: Sporadic patches of giant ragweed (Ambrosia trifida) are emerging above the grassline in field edges mostly along ditches and not within field margins. Let your neighbors know if you spot giant ragweed and where as they are not easy to find amongst all the other weeds along ditches.

 

Palmer amaranth: Pigweeds, mostly palmer amaranth (Amaranthus palmeri) along field crop margins are rapidly growing and are one of the more frequent observations along outside rows adjacent to lawns and sensitive crops in Salem County. For resistance management, these outside rows of half-dead, curled but still living plants are where resistance can develop. If already sprayed, mow these down to the ground or till under even if it means sacraficing the outside row of crop. If sprayed or mowed, monitor the area to make sure pigweeds completely die.

Ivy Leaf morning glory: Ivy leaf morning glory (Ipomoea hederacea) will continue to sprout with this flush of rain. Monitor newly planted double crop soybeans into wheat stubble for flushes moving into fields from field edges.

Marestail: Over all marestails (Conyza canadensis) are under control except in fallowed unplanted and untilled fields with last year’s crop residue still present. Brushog these down before notilling. Marestail is a wind dispersed seed that like thistles, will end up infesting hundreds of acres downwind if allowed to go to seed.

Thistles: Thistles in the Cirsium and Carduus genus are sporadic but on some idled fields extensively spreading by root rhizomes (Canada) and seed dispersal (Bull, Musk). Canada thistle in sandy soils is a life time headache greatly increasing field management costs over time.

June 26, 2021

A field of ready to harvest wheat was observed infested with 4^th to 5^th star grasshopper nymphs in Salem County. While waiting for positive identification from entomologists familiar with the differences in the nymp identification, these nymphs appear to be differential grasshoppers (Melanoplus differentialis). The uniform yellowish color of nymphs observed, is an indication the population is quite high. Lesser populations tend to be more green in color. Additional fields of wheat, corn and soybean on the same farm all had nymphs present but were not at economic threshold yet.

Visual counts observed walking into the field were more than 4 as they hopped away fro

m a square foot area, repeated in multiple locations. This confirms the population is very high. The threshold for nymph stage grasshopper populations causing economic injury is 15 – 20 per square yard. (Four or more per square foot; nine square feet in a yard = more than 20 per square yard = high infestation.)

Because grasshoppers move from preferred forbs like alfalfa and hay fields, and field edges, into cereal crops it is recommended each cereal grain field not yet ready to harvest due to high moisture content be observed to assess thresholds.

When grasshopper nymph levels are this high, the damage to unharvested cereal grains can be concernin if the adult phase coincides with near ready moisture crops, because their feeding can clip the dried grain head stem and both phases chew on seed head grains.

There is no standard for the level of clipped seed heads per say. Monitoring is the best method to determine if harvest will resolve the issue or if a foliar insecticide is needed to protect the grain quality and yield.

The active ingredient Rynaxypyr (Chlorantraniliprole, IRAC 28) found in Dupont insecticide Coregen and FMC’s insecticide Prevathon are labeled for foliar application of grasshoppers in multiple vegetable, field and forage crops.

“Growers can make a foliar application of Prevathon insect control by ground, air or overhead sprinkler chemigation. It has a short re-entry interval of four hours, a favorable worker protection standard profile and a short PHI.” – FMC website, https://ag.fmc.com/us/en/insecticides-miticides/prevathon-insect-control

Once wheat is harvested, grasshoppers will fly to corn and soybean and alfalfa regrowth. Japanese beetles were present in these crops but currently at low levels. Feeding damage may be misidentified as japanese beetle damage when it is actually an indication of grasshopper pressure building. Nymphs were present in adjacent corn and soybean fields but at low levels.

Monitor soybean and young corn fields closely for signs of adult grasshopper feeding through August. Note that a dense swarm of differential and two-striped field crop grasshoppers can destroy the leaf area of a crop in just a few hours.

The following links have useful identification and detailed management recommendations for various stages of grasshoppers on various crop stages of development. The soybean research link shows the defoliation thresholds in soybeans.

Identification https://www.youtube.com/watch?v=bgi6De5NDIw

Identification https://www.youtube.com/watch?v=bgi6De5NDIw

Identification http://idtools.org/id/grasshoppers/factsheet.php?name=13190

Economic importance  http://idtools.org/id/grasshoppers/factsheet.php?name=13190

New Jersey species in 2005 https://njaes.rutgers.edu/pubs/publication.php?pid=fs290

Coragen label http://www.cdms.net/ldat/ld8KF045.pdf

Soybean reasearch https://soybeanresearchinfo.com/soybean-pest/grasshoppers/

Prevathon label https://ag.fmc.com/us/en/insecticides-miticides/prevathon-insect-control