Update on Dry Conditions for Crops

By: Bryant Spivey
County Extension Director
Johnston County Cooperative Extension

About 2 weeks ago, I wrote an article regarding drought conditions for crops in Johnston County.  If you read it you will recall that our crops depend mostly on the moisture in the top 12 to 24 inches of the soil.  Two weeks ago, the moisture in that part of the soil profile was very, very limiting and crops needed rain badly.  Since that time, we have experienced favorable rainfall in many parts of Johnston County.  However, we still have places that need more rain.

Damage to Crops

The dry weather that we experienced in late June and July has adversely affected crops in Johnston County.  There is no place that this damage is more evident than when you drive by a local corn field.  Plant breeders have improved drought tolerance in corn, but this crop desperately needs rain during pollination.  Without moisture during pollination, there will be poor pollination and missing kernels on the ear.  In addition, ears and kernels will be smaller under dry conditions.  Corn that was in the pollination phase during the dry conditions – a good portion of the crop – is severely damaged.  I have heard of a few fields in Johnston County that are nearly a total loss especially in the driest locations.

With soybeans and other crops the situation is a bit different.  Soybeans can withstand drought conditions somewhat better than corn, but they do not escape completely.  Soybeans are short-day plants meaning that they are triggered to flower as the daylight hours decrease to a critical point.  The plants grow in a vegetative phase until the days reach a critical day length and then they enter a reproductive phase.  Once the plants begin to flower, further vegetative growth is very limited.  This is important, because ideally, we need our plants to reach a height of about 36 inches.  As you know, the longest day of the year is the first day of Summer, and each day thereafter we get less light and soybeans begin to flower.  While we were dry in June and July, we missed the period for optimum vegetative growth.  So, in many cases our plants will be less than the optimum height and ultimately will produce fewer harvestable beans.

Crops like cotton and peanuts are indeterminate plants that will can flower over a long period of time.  In good years, we will have up to a 7-week effective bloom period in cotton and the plant can set a good fruit load in as little as 2-3 weeks. Peanuts have a similar pattern but the later this good weather occurs, the later that pods or bolls are set and then the later the crop will be when it reaches maturity.  Cool temperatures in the fall begin to slow development of peanuts and cotton making it difficult to mature and harvest crops in a timely manner.

One reason why we grow tobacco – drought tolerance!

In the last article, I mentioned our well-drained, sandy soils.  These soils work well for tobacco which needs excellent drainage for the root system.  Excess water can cause wilting due to oxygen depletion, leaching of nutrients, and even promotes pathogens that attack tobacco plants.  However, when it gets dry our crops suffer. Tobacco is however, extremely drought tolerant.

During dry periods, the plant goes into a defensive state with the lower leaves lifting upright to protect and shield the younger more critical leaves.  The plant essentially slows down and waits.  And then when the rain comes the plant resumes growth. Since the rains have come, in some locations the tobacco crop has responded tremendously.  The upper leaves have grown and filled out and put on a good bit of weight.  Lower leaves have been severely damaged by the heat and dry conditions.  In many fields, we lost 4-6 lower leaves due to the burning.  However, these are the least valuable leaves on the plant.  Growers know this, and in many cases, have removed these lower leaves due to the damage.

Now tobacco has not escaped entirely.  It is the last day of July and a very small percentage of our crop has been harvested. In a normal year, many farmers will begin harvest around July 4th.  This was delayed 2-3 weeks this year and farmers have started harvesting slowly.  They did this because the crop was just not ready.  Tobacco must be mature and ripe and it needs rain to reach this stage.  Now with the rain the crop has returned to a growth stage.  It is immature in many cases and it is green (not ripe).  So now, growers must wait even longer to begin harvest in earnest.  This can be a major problem.

Growers own the equipment necessary to harvest the tobacco crop making use of the time from July 4th to about October 15th.  It takes on average 8-10 days for each cure in a tobacco barn.  Typically, each barn on the farm needs 8 to 10 cycles to harvest the entire crop.  So, it will take 80 – 100 days to harvest a typical tobacco crop. If you start harvest on July 23rd it is only 84 days until October 15th and 91 days until October 22nd. Now you know things will never work out just right over a 90-day period.  There will be days that are unsuitable to work and we are really not ready to begin in earnest because our tobacco is not mature and ripe.

To put is shortly, we need a late frost and good weather from here on out.