Rainfall last week was welcomed across the region and relieved the anxiety for those with crops planted into dry soils and for growers waiting for some activation of soil applied herbicides. Crop heat unit accumulation since the beginning of May is about 425 CHU. This is close to last year and long-term average, with cooler temperatures at the beginning of the month slowing a trend from April that was ahead of normal.
Frost damage over the weekend was limited to mostly tissue damage in southwestern Ontario, but more severe damage moving north. Corn crops are showing the most damage, even though the growing point is still below the soil. The change in temperature with several near 0oC nights followed with bright sunshine resulted in a tremendous amount of sunscald leaf damage. Soybean crops, although more vulnerable, do not appear to have frost damage except in a few high residue fields and in some organic soils. For wheat crops in this region, there is some evidence of head snag, but no bleached heads. Where temperatures were coldest, the wheat was still in boot stage where temperatures down to -2oC can be tolerated. Colder temperatures (further north) resulted in more significant damage.
Wheat is shorter than normal but there have been no reports of lodging except in a few highly managed fields. Wheat growth slowed through the cool weather and delayed timing for fungicide application in some fields. Many wheat fields will be at the proper stage for T3 fungicide applications this week. Some fields had T3 fungicide application last week. Powdery mildew is progressing above expectations, especially in susceptible varieties and should be monitored for fields that are still a few weeks away from T3 fungicide application. Stripe rust has been identified in a few areas of Ontario – some around Seaforth and some around Aylmer and Dutton. Stripe rust infections seem to be closer to the lake. Highly susceptible varieties that are still 10-14 days away from T3 application may need an application before T3 timing. Moderate or highly resistant varieties probably have some flexibility, but it is still important to scout. Stripe rust disease progression slows down with temperatures (over 25oC) but new variants – heat tolerant races – may be able to withstand higher temperatures.
Forage harvest is underway with more fields cut and harvested in May than usual. Orchard grass and Italian rye have headed, and alfalfa is in bud stage. The crop is shorter than normal, but also very thick and yields and quality are good. Alfalfa weevil numbers are very high in some areas and seems to be area and older stand specific. The silver hue of a field with alfalfa weevil-damaged is very evident. Earlier harvest is occurring in the Haldimand-Niagara area, where normally they harvest 2 cuts, just to reduce weevil impact. Some spraying to control weevil has occurred in the Brigden area. Colder temperatures have not slowed weevil feeding. Scouting should occur for fields where harvest is not planned for a few weeks.
Corn fields everywhere are exhibiting the effects of cold temperatures. Most fields are in the “ugly phase of corn”, where between V2 and V4 stage when roots are transitioning. The cold temperature damage just makes it more visual. Corn growth has slowed and there may be some symptoms of purple corn syndrome, but overall optimism continues for a good corn crop.
Soybean emergence was rapid for fields planted in the second half of May. There was observed speedier emergence of conventional soybeans compared to those planted into residue, due to cool temperatures but bright sunshine. Even within high residue fields, there is more variable emergence than usual due to soil moisture variations at planting. In fields that were chiseled, the dry soil was moved into the valleys between the ridges, leaving some seeds planted into dry soil and resulting in interesting field patterns of emerged beans. Some growers that were planning to roll soybeans at 1st to 2nd trifoliate, but now have late soybeans emerging after recent rains
Herbicide applications to corn crops should ideally be delayed for about 72 hours following frost, however with some weeds at a growth stage where applications shouldn’t be delayed, wait at least 24 hrs. Crop injury occurs with herbicides when the cuticle is thin and they can absorb more herbicide – often seen with bromoxynil-based herbicides, and when the plant isn’t growing quickly enough to metabolize the herbicide. Herbicides such as glyphosate are relatively gentle for the crop compared to dicamba based herbicides that tend to be more unpredictable and circulate in the plant for a period of time that can affect growth later in the season.
The question about rainfall over the weekend being enough to activate soil-applied herbicides led to some interesting observations from Peter Sikkema and Francois Tardiff. If soil was powder dry when herbicides were applied, they need more rain to be activated compared to herbicides applied to soils with relatively good soil moisture conditions. Weeds that escape the pre emerge treatments will be the weeds the herbicide is weakest on. Difference in activation depends on active ingredient, soil type, weed species and other factors. There is difference in herbicide groups and there are many variables but from experience Group 15 herbicides take more rainfall to activate than most other soil applied herbicides. Francois suggest the same seems to occur with Group 27 herbicides.
The level of activity for grass and broadleaf control from pre emerge treatments compared to control treatments is still amazing. Post emergent weed control is a field-by-field decision and should be based on weed density and stage of the weeds. Small weeds in a larger crop are not as competitive and there is time for control. Where the crop and weed at the same height, they should be controlled as soon as possible to avoid yield loss from competition. Broadleaf weeds are much more competitive with corn and soybeans than annual grasses. Minimum tillage seems to leave more dandelions and burdock.
Supply of pesticides – herbicides and fungicides – are tight but there should be alternatives, even if it isn’t the first choice of product.
No frost injury was observed to tomato or sugar beet crops. Injury from sand blasting on tomatoes is mostly moderate and will slow herbicide timing a bit. Herbicide application made shortly after the frost only caused damage on high sands. Rain last Friday helped germinate some seeds in dry soils – uneven germination. The rain was very timely for crops planted into heavy cover crop cover. Rain, accompanied with the cooler temperatures was especially timely for peas crops. Cool weather during pea flowering period is critical for high yield.
Frost damage reports have started to come in from some areas; however, the consensus was that it could have been a lot worse. As of May 28th there were 114 winter wheat damage reports covering 7,300 acres and 38 corn/soybeans reports covering 2,800 acres. Impact of frost has not been reported by Agricorp yet but so far damage reports are lower compared to previous years.
Planting report deadline is June 30th for soybeans and June 15thfor corn. Replant benefits – $122/ac for corn and soybeans $92/ac. Contact an agricorp adjuster and submit a damage report as soon as possible when damage occurs. Replant benefit covers average cost of seed tillage and planting. The adjuster will look at the damaged field although they also recommend having it checked by a CCA if possible. The adjuster will give go-ahead for reseeding; then let adjuster know when replanting was done to complete paperwork for payment.