Last week we discussed in our agronomic crop report about moisture stress in crops from too much rain. This week, we have certainly flipped the script as we are dealing with a flash drought. In a recent Crop Observation and Recommendation Network (C.O.R.N.) article by Taylor Dill and Jamie Hampton, it was shared that we can actually calculate at what point we may see damage from the heat and drought stress in our crops. When temperatures exceed 86 degrees, you can calculate those periods as stress degree days. Once corn reaches 140 stress degree days, the chance of reaching above average yields begins to decrease. Dill and Hampton also point out that “Leaf rolling is a common symptom of high-temperature stress. Yield diminishes by 1% for every 12 hours of leaf rolling during vegetative growth but increases to 1% every four (4) hours during silking. When water is deficient during a heat wave the loss of yield increases after four consecutive days of 93°F or above, not including the stress from leaf rolling. So, the impact of heat stress can be two-fold.”
Soybeans are in a similar situation, as shared in the article by Dill and Hampton. “Soybeans have a similar range in temperature to corn for heat stress. Temperatures above 85°F for several consecutive days can cause heat stress. This heat can accelerate maturity because soybeans are photoperiod and temperature-controlled when it comes to flowering. During vegetative stages, these high temperatures can slow or stop photosynthesis because the plant is making an effort to conserve water. Thus, inhibiting new vegetative growth, which is vital for late-planted soybeans. Temperatures above 86°F can also reduce nodulation and therefore N-fixation in the soybean which could have an effect until the reproductive stages.”
Japanese beetles were found in agronomic crops this week. Potato leaf hoppers are present in alfalfa; however, our scouting did not find any significant populations.
Now is a critical time to be monitoring your cucurbit crops for cucumber beetles. Early populations may not seem as evident due to the presence of insecticide in treated seed, however, as the efficacy of the seed treatment diminishes, the cucumber beetle feeding will begin to increase. The threshold for beetles while the plants are in the 2-4 leaf stage is 1 beetle per plant. Once the plant is above the 4-leaf stage, the threshold increases to 3 beetles per plant. The greatest chance for impactful feeding damage and bacterial wilt infection via the cucumber beetle occurs during early season feeding.
Also, of note in cucurbits, the excess moisture and warm conditions allowed for development of some phytophthora cases. If you suspect that you have plants infected by this pathogen, avoid spreading it in your fields by removing and destroying infected fruit and plant material. An integrated approach to managing this disease includes practices such as avoiding excess water, sufficient crop rotations and fungicide treated seed. Additional findings in cucurbits included squash bugs being found this week in an early planting of yellow squash.
Continue to monitor onions for thrips populations. The recent heavy rain may have prevented populations from building, however, hot dry weather, combined with the increased size and number of leaves can provide the opportunity for thrips numbers to escalate rapidly.
In tomatoes our scouts noted some observations of early blight and Septoria.
Remember to check your crops for any signs of foliar diseases, especially with the amount of soil splashing that took place in the last few weeks. Bacterial and fungal diseases can be spread on the lower leaves of plants when heavy rains splash soil and pathogens onto the foliage. Overall, stress from high temperatures has been evident in a majority of the crops that we are scouting.
Small Fruit and Orchards
Spotted winged drosophila have been caught in traps around Wayne County. As we move out of strawberry season into raspberries/blackberries/blueberries, the SWD populations will begin to increase leading to possible infestations in ripening brambles and blueberries.
In apples, we continued to find strikes of fire blight. Conditions have been ideal for fire blight development, although dryer conditions may hinder further development. This week we continued to find aphids in apple trees. Our IPM program identified populations of green apple aphids in several orchards as well as a case of wooly apple aphids. Both aphid species can cause significant damage at this time of year. Accordingly, diligent scouting is a crucial aspect to not allowing either of these aphid species from getting out of hand. The heavy rains likely knocked back some of these aphid populations, but it will be important to monitor aphid populations as dry conditions take hold.
We have had sustained catches (over threshold) of both Codling Moth and Oriental Fruit Moth in apple and peach orchards, respectively. Over the last week, both Codling Moth and Oriental Fruit Moth populations have been trending downward, however, numbers have still exceeded the thresholds.
Now is the time to be managing early season diseases in apples. Scab, rust and powdery mildew are the three main diseases of concern at this point in the season.
Once strawberry harvest is over, it is a good time to consider renovation of the patch. the goals in renovation are to reduce plant numbers by narrowing the rows, remove old foliage (reduces diseases), control weeds, and reduce insect pests. After renovation, regular irrigation and weed control are essential. High yields next year depend on having large, healthy, vigorous plants when fruit buds are initiated in late summer
Grapes are currently around the buckshot berry stage. It is still possible to spray for and manage black rot during this time. We have started catching grape berry moth in our traps.