As of July 19, it's been over three weeks since many have recorded any significant rainfall, and temperatures have been in the 90s for most of that time period. We've gone from an almost record amount of rainfall in June to (thus far at my house) 0.2 inches in July. And yet for the most part crops and plants look great.
Corn planted prior to early-mid May has completed pollination, and May-planted soybeans are blooming.
Some are questioning the effect the heat will have on crops.
In spite of those frequent rain events of June, crops and plants have apparently developed a good root system. Otherwise we'd be witnessing stress in these crops (rolling of corn leaves and wilting of soybean). So the plant root system is still able to uptake the quantity of water necessary for the continued growth of the crop. But at some point, and the sooner the better, we're going to need additional moisture to prevent abortion of kernels.
While excessively high temperatures can sterilize pollen, those temperatures aren't reached until mid-afternoon. Pollination normally occurs during the early part of the day, so as long as the later-planted corn crop continues to look good, pollination probably won't be an issue.
The later-planted crops are the ones to be most concerned about. They don't have the amount of root system of the older plants, and in some cases, their small size is allowing sunlight to reach the ground which is heating up the soil, making for a tougher environment for root systems with higher temperatures and lower soil moisture.
As water and nutrients enter the root system, they are conducted throughout the plant. Water is "evaporated" out of the plant through a process called transpiration. It is estimated that an acre of corn can transpire 3,000-4,000 gallons of water per day. This is an essential plant mechanism. Plants also respire, which is the process of burning sugars during the night for cell growth and maintenance. As temperatures increase, respiration increases, which reduces the amount of sugars the plant can use for grain. So high temperatures can reduce yield, via increased respiration, as well as transpire higher levels of water.
Corn leaves roll to help the plant reduce transpiration (water) loss. It's a protective mechanism to help the plant cope with dry soils. The plant suffers no harm if this occurs for a short time, but if it occurs daily or for the majority of the day for a period of time, it's a signal the plant can't get enough water to function and is shutting down, which isn't good.
Most of the crops are of good size, and tall crops help shade the soil, reducing soil temps. The crop looks much better this year than last, and apparently has a fairly well developed root system, as we haven't seen much in the way of stress in either corn or soybean. As long as these temperatures don't persist and moisture doesn't give out, our corn and soybean crop won't be irreversibly damaged by the high temperatures. But the fact remains, both corn and soybean crops would perform better with temperatures in the upper 80s, not upper 90s. And so would I.
Lawns and gardens are taking the heat and dry weather a little harder than the crops. You can see the grass turning from a deep green to a faded green. Grass is a cool season crop, so these high temperatures combined with low rainfall have put it into a stress condition. Most unwatered bluegrass lawns will simply go dormant and wait for cooler and wetter weather to arrive. Fescue lawns also will slow growth waiting for better conditions.
If you're going to water, you'll need to follow correct procedure. First, make sure you water only once per week (unless we continue to get 100 degree temps, then twice per week), but water deeply and apply one inch per watering. Best to water early in the morning versus late afternoon. The same rules would apply to the garden, and for garden, drip or soaker hose would be preferred to overhead sprinkling to reduce fungal disease spread.