Several farmers in North Alabama have reported a large number of squares and small (two-day-old) bolls being shed following large amounts of rainfall last week. Although no one enjoys seeing this, it is not surprising considering recent conditions of the cotton crop and environment.
This is the lightest plant bug year I can remember in sometime and much of the crop had 90% or greater fruit retention up to this point. Cotton will seldom hold 90% of its fruit even under ideal conditions, and it is not uncommon for a cotton plant to shed 40-60% of its fruit under normal growing conditions.
Fruit shed can be caused by a host of factors such as insects, nutrient deficiencies, environmental conditions, and pathogens. As mentioned before, environmental conditions are likely the cause for this in most situations over the last week.
Carbohydrates or photosynthates accumulated in the leaves are responsible for “feeding” developing bolls. Environmental stresses reduce the plants ability to meet carbohydrate demands for these young developing bolls. Cloudy conditions with lack of sunlight have accompanied recent rains reducing photosynthate production, thus resulting in fruit shed.
Cotton under a heavy boll load may not be able to produce enough photosynthates to meet the demand of its existing fruit load under these conditions. The cotton plant gives preference to older more mature bolls and sheds the youngest fruit. When this is coupled with high temperatures and humidity, this places more stress on the plant and can escalate the situation.
As soils become waterlogged, photosynthates in cotton plants are reduced due to lack of oxygen, which will also result in fruit shed. Many fields were extremely dry leading up to last week’s excessive rains. When prolonged drought occurs followed by a rainfall or irrigation event, fruit shedding often occurs due to the previously mentioned stresses and factors.
Fruit shed may be worse where cotton is rank, seeding rates are too high, and excessive nitrogen was applied. This is due to lack of sunlight penetration into the canopy. Shading of lower subtending leaves (leaves closest to the fruit) will reduce photosynthate production and can cause shedding.
Several have noted that they have observed greater fruit shed on 30 inch row cotton versus wider row and skip row cotton. This stands to reason due to the tighter canopy and shading created by narrower rows.
On a positive note, much of the crop still has a more than adequate boll load. Furthermore, yield potential remains good for many areas despite what may seem like excessive fruit shed.