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Crop water use (transpiration) during the growing season is a major factor in attaining high yield potential. Soil water loss (evaporation) and crop water loss (transpiration) occur simultaneously; making predictions of evapotranspiration complex. Actual evapotranspiration values vary greatly from day to day (0.04 to 0.40 inches/day) because of the following factors:
Corn roots grow rapidly starting at the 4th-leaf stage and continue throughout vegetative development. This typically occurs from June to early July. Several factors affect root growth, but temperature and soil moisture are the most relevant factors in the absence of soil constraints. Well-developed, deep root systems are essential to support water and nutrient uptake and thus high yield potential. Hot and dry weather results in a depletion of moisture in the top 6-inch soil layer.
Oak tatters is a disorder that primarily affects white oaks, but also is observed on hackberry trees. Leaves of affected trees lose the majority of interveinal leaf tissue, resulting in a leaf ‘skeleton' (Figure 1). The phenomenon was first reported in the early 1980’s, and has been observed in many Midwestern states. The number of trees affected varies widely from year to year, with a much higher level of incidence in 2017 than normal. The disorder occurs in both rural and urban areas and may affect single trees and those in woodlands. Symptoms usually are distributed uniformly throughout
Japanese beetle is an invasive insect capable of feeding on corn and soybean. This pest has been in Iowa since 1994 but its distribution in field crops is sporadic around the state. Statewide populations have been low since 2014 and it is unclear if pressure will be significant this year. Japanese beetle adults need about 1,030 growing degree days (base 50°F) to complete development and will continue emergence until around 2,150 degree days. Based on accumulating degree day temperatures in 2017, Japanese beetle adults should be active in some areas of southern Iowa this week (Figure 1).
Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. In 2017, the average hatching date will be about the same time as the 2014-2016 growing seasons. Development is driven by soil temperature and measured by growing degree days. Research suggests about 50 percent of egg hatch occurs between 684-767 accumulated degree days (base 52°F, soil). Most areas in Iowa have reached peak corn rootworm egg hatch or will within a few days (Figure 1).
Tracking degree days is a useful tool to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications, if needed, are only effective when larvae are migrating and exposed. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Southern Iowa counties reached this important benchmark over the holiday weekend (Figure 1), and therefore scouting for migrating larvae should begin now to make timely treatment decisions.
Lately it seems to be an annual question with no exception this spring – has there been nitrogen (N) loss from my applied N? That question should also include what has been the N loss from the soil N supply or residual nitrate-N. There is usually tile drainage every spring and sometimes but not usually in the late fall (remember a couple of years ago). Also, losses if soils become saturated (free water filling the soil pores, standing water, anaerobic conditions) and soils are warm then denitrification happens (biological conversion of nitrate to N gas).
The Iowa Department of Agriculture and Land Stewardship (IDALS), ISU Extension and Outreach Pesticide Safety Education Program, and the Iowa Agribusiness Association of Iowa want to remind pesticide applicators in Iowa that IDALS’ Sensitive Crop Directory has now partnered with the nonprofit company FieldWatch, Inc. to offer producers two online registries for sensitive crops and apiaries with a third online registry for applicators to view and download producer entries. These registries replace the former Iowa Sensitive Crop Directory.
A new ISU Extension and Outreach publication, Use of the Late-Spring Soil Nitrate Test in Iowa Corn Production (CROP 3140), has replaced the previous publication (PM 1714). The publication is available from the ISU Extension Store.
The potential for herbicide injury with preemergence herbicides is greater with soybean than corn. The risk increases with environmental conditions that reduce crop vigor and growth rate, and also with heavy rain that moves the herbicide to the depth of the germinating seed or emerging seedling. Much of the state has experienced these conditions, thus it is likely symptoms will be found in many fields as people return to the field with the improved weather.
