H.Y. Hanna

Root-knot nematodes cause significant yield losses in many horticultural crops. Recent estimates indicate nematode injury to cantaloupes in the United States exceeds $40 million each year. Development of commercial tomato cultivars resistant to root-knot nematodes has reduced the risk of losses from this pest without environmental damage; however, no cantaloupe cultivars with high resistance to root-knot nematodes are commercially available to provide similar protection. Cantaloupe growers use nematicides to control this pest, but use of these pesticides may be restricted or eliminated in the future.

The Norwood sandy loam soil prevalent in the Red River Valley in northwest Louisiana is prone to nematode buildup because of continuous farming with susceptible crops such as cotton. The number of root-knot nematodes found in plots previously planted with nematode-resistant tomatoes was significantly lower than the number found in plots planted with susceptible tomatoes. Our earlier research indicated that double-cropping cucumbers with nematode-resistant tomatoes can be a viable alternative to soil treatment with nematicides to improve cucumber yield in soil infested with root-knot nematodes.

The long growing season in the South offers the potential for double-cropping mulched and drip-irrigated beds. Double-cropping tomatoes with cucumbers or other members of the cucurbit (gourd) family reduces production costs because succeeding crops use the existing polyethylene mulch, drip tape and fertilizers applied to the first crop. Black polyethylene is preferred for growing spring tomatoes because of its warming effect on the soil, but heat accumulation under the black mulch during sunny days in mid to late summer or early fall limits its use for double-cropping. This experiment was conducted to compare nematode-resistant and susceptible tomato cultivars mulched with black or white polyethylene on growth and yield of succeeding crops of cantaloupe.

Studies were conducted in 1996 and 1997 on a Norwood sandy loam soil at the LSU AgCenter Red River Research Station in Bossier City. Celebrity (nematode-resistant) and Heatwave (nematode-susceptible) tomatoes were transplanted on black or white polyethylene-mulched and drip-irrigated plots (raised beds) in early April of each year. Fertilizer rates and other cultural practices consisted of standard recommendations for growing staked tomatoes for fresh market production.

Following plant removal after the last harvest of tomatoes in early July, the plots were sprayed with a herbicide (glyphosate) at 3 pounds per acre. Athena cantaloupe seedlings were transplanted into tomato plots during the third week of July in both years. Cantaloupes were double-cropped with both nematode-resistant and susceptible tomato cultivars and were mulched with both black and white polyethylene. Cantaloupes were harvested and evaluated for grade according to U.S. Department of Agriculture standards and then weighed. Fruit that were well formed, well netted and free from decay, damage and sunscald were graded as marketable. Fruit that were deformed, cracked, rotten or weighed less than 1 pound were culled. All plants in each plot were removed after the last harvest, oven-dried and weighed. Healthy roots were separated from galled ones, and the percentage of galled roots was calculated.
 
Cantaloupes planted after the nematode-resistant tomato cultivar Celebrity produced significantly higher marketable yields and more fruit per acre than did those planted after the nematode-susceptible tomato cultivar Heatwave in both years. Percentage of culls was not significantly affected by treatment in either year. Plant dry weight was heavier and percentage of galled roots was smaller for cantaloupes planted after the nematode-resistant than after the nematode-susceptible tomatoes. Mulch color had no significant effect on cantaloupe marketable yield, fruit number, percentage of culls, plant dry weight or percentage of galled roots.

This study indicates that double-cropping cantaloupes with a nematode-resistant tomato cultivar can improve cantaloupe yields in soils that have a history of root-knot nematode. Study results also indicate that growth and yield of cantaloupes were similar when planted on black or white polyethylene mulch.

H.Y. Hanna, Professor, Red River Research Station, Bossier City, La.