Cooperative Extension Service
College of Agricultural and Environmental Sciences
The University of Georgia

Volume 4/Number 5

May 2000

George Boyhan, Extension Horticulturist-Vegetables
East Georgia Extension Center
Rosenwald Building, Third Floor
PO Box 8112
Georgia Southern University
Statesboro, GA 30460
912-681-5639 | 912-681-0376, Fax | 912-682-3481, mobile

Fertilization Under Plastic

More and more growers are producing vegetables on plastic with under-plastic drip irrigation. With this method of growing vegetables, it is possible to apply fertilizer injected into the drip system. This is often referred to as fertigation. This method of fertilizer application has many advantages over broadcast or banding. To begin with, there is little waste. Broadcasting in particular can be wasteful of fertilizer, since much of the material is not used by the plant. Banding can be tricky if you aren't careful with placement. It is easy to kill or injure seedlings and small plants without proper placement.

Fertigation is extremely fertilizer-use efficient. Applications of fertilizer by this method are measured in pounds per day or per week. This means that the fertilizer is applied each day or every couple of days over most of the growing season. Plants are never stressed for lack of fertilizer.

I spoke with John Meeks of Griffin Fertilizer in Douglas, Georgia, about liquid fertilizer availability and cost. They sell several liquid products in bulk and can formulate custom fertilizer blends as well. They also have dry material that is water soluble, such as KNO₃, CaNO₃, and 20-20-20. When you buy CaNO₃, make sure you get greenhouse grade or a similar material. CaNO₃ for field application has ingredients to help it flow, but when you mix it with with water, it forms an insoluble scum that won't go into solution and can clog emitters.

Liquid bulk items Griffin Fertilizer has for sale include 18-0-0, 10-34-0, 3-0-12, CaNO₃, 28-0-0, 32-0-0 and 19-0-0 (NaNO₃ ) with prices ranging from $65 to $225 per ton. Generally, they sell in 5-ton lots or approximately 1,000 gallons. Smaller quantities (by the gallon) of some items such as 16-0-4, 8-0-8 and foliar urea are also available. Smaller quantities of water-soluble fertilizer are available through greenhouse and nursery wholesale suppliers as well.

New Research in Florida Offers New Hope in Control of TSWV in Pepper

Tomato spotted wilt virus is rapidly becoming the limiting factor in tomato and pepper production. This virus is spread by thrips. Once a plant is infected with the virus, nothing can be done. Symptoms can be very variable from stunted growth, mosaic and ring patterns on the leaves, ring patterns on the fruit, and leaf curl.

Attempts have been made to control this disease by controlling the vector (thrips) but with only limited success. Several different insecticides and insecticide combinations have been tried. On pepper, for the control of western flower thrips, Monitor, Spintor, Baythroid, Orthene, and Lannate are currently available for control.

Recent work at the University of Florida has shown that minute pirate bugs (Orius insidiousus) are excellent predators of thrips. A ratio of 1 pirate bug to 200 thrips gave suppression, and 1 pirate bug to 40 thrips resulted in rapid extinction of thrip populations.

Using insecticides that do not harm these predators (such as Spintor) helps suppress thrips while allowing the biological control of the pirate bugs to have maximum effect. We hope this kind of integrated approach will minimize this devastating problem.

From My Desk

The onion harvest is complete, with good quality across the onion belt. Overproduction and high yields resulted in low prices. I heard of prices in the $6 to $8 per 40-pound box range not very long after the market opened. We did finally get some scattered rain in southeast Georgia. I heard from 0.5 to 1.0 inch, but plenty of people got none. The pepper story is based on "Integrated Management Tactics for Thrips and Tomato Spotted Wilt Virus in Pepper," which appeared in the University of Florida's publication NFREC Extension Report No. 2000-1. This report was compiled as part of the North Florida Research and Education Center field day held on June 1, 2000. Talk to you next month (actually later this month).