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» Double cropping vegetables can result in increased nematode pressure for the second crop.
» Soil fumigant and non-fumigant nematicides can help manage nematodes in both first and second crops in a double-crop system.
» Planting first-crop vegetable varieties with resistance to nematodes can help reduce the nematode pressure on the second vegetable crop.
ADVANTAGES AND DISADVANTAGES
Double cropping is the practice of successively planting two crops in the same location in a single season. Common vegetable double-crop systems in the southern U.S. include pepper or tomato, followed by cucumber, melon, or squash. One of the advantages of double cropping is increased revenue of two crops from the same plot of land in a single season. With vegetable crops grown in a plasticulture system (plastic mulch with drip irrigation on raised beds), the costs of plastic mulch, drip tape, preplant pesticides, and the labor costs associated with bed establishment are spread over two crops. After the final harvest of the tomato or pepper crop, those plants are removed, and seeds or seedlings of the following cucurbit crop are sown or transplanted into the same mulched beds. Many plasticulture systems also use pre-plant soil fumigation to help manage soilborne diseases and weeds, and the benefits and costs of fumigation can be spread over the two crops.1
There are also disadvantages of using double-crop systems for vegetable crops, primarily the potential for increased damage from soilborne diseases and pests in the second crop. If not managed properly, pathogens that have wide host ranges, such as root-knot nematodes (RKN), can build up on the first crop and more severely infect the second crop. Higher soil temperatures during production of the second crop can also result in shorter pathogen disease cycles and infection of the second crop at earlier physiological stages.1
VEGETABLE NEMATODES
Vegetable-infecting nematodes include root-knot nematode (Meloidogyne spp.), stubby root nematode (Paratrichadorus minor), sting nematode (Belonolaimus longicaudatus), and root-lesion nematode (Pratylenchus penetrans). Root-knot nematodes, in particular, can be very damaging and a major constraint for vegetables grown in double-crop vegetable systems (Figure 1). Five species of RKN occur on vegetables in North America; Meloidogyne arenaria, M. enterolobii, M. hapla, M. incognita, M. javanica, and M. enterolobii. Of these, M. incognita is the most common. Multiple species of nematodes can be present in the same field and infect the same plants.1,2,3

NEMATODE MANAGEMENT
Nematicides: Soil fumigation has been a primary method to help manage nematodes in vegetable crops. Preplant fumigants include 1,3-D, metam sodium, and chloropicrin. Depending on the product, soil fumigants can be applied using chisel injection or through the drip system (chemigation).1 Preplant fumigants applied before the first crop may help reduce damage from nematodes, such as RKN, for both the first and second crops.1 Non-fumigant nematicides (such as fluopyram, fluensolfone, fluazaindolizine, and oxamyl), applied to the soil or by chemigation, can also help reduce the damage and yield losses associated with nematode infections.1,2
A study on nematode management in Georgia on double cropping, with eggplant or tomato as the first crop and cantaloupe, squash, or jalapeno pepper as the second crop, found that fumigation with chloropicrin, 1,3-D, and metam sodium resulted in lower levels of nematode damage and higher yields on both the first and second crops.1 All of the preplant fumigant treatments provided some control of nematode damage and average yield increases in the second crop of 10 to 15% for cantaloupe. The non-fumigant nematicide treatments provided additional nematode control for some, but not all of the second crop species. Post-plant applications of nematicides were more beneficial to the second crops than to the first crops in this study.
In some studies, however, the application of some fumigants before planting of the first crop resulted in greater damage and yield losses in the second crop due to nematode infections.2 A study on nematode management with tomato as the first crop and cucumber, squash, zucchini, or cantaloupe as the second crop found that preplant fumigation treatments containing chloropicrin resulted in higher levels of root damage from RKN in the second crop in seven of ten trials. Yields in the cucurbit crops were also higher in the non-fumigated plots in four of the ten trials. It was hypothesized that chloropicrin, which is more active against fungi than nematodes, might have affected the naturally occurring nematode-suppressive microorganisms in the soil, allowing for more infection by RKN. One of the non-fumigant nematicide treatments (fluensolfone) of the first crop resulted in lower RKN on the second crop. The other nonfumigant nematicide treatments of the first crop did not affect the severity of RKN damage on the second crop.2
Host Nematode Resistance: Planting vegetable varieties with resistance to nematodes (mostly RKN) as a first crop may lower the level of nematode damage on the second crop in double crop systems. Planting first-crop varieties with forms of resistance that lower the rate of nematode reproduction can result in lower soil population levels of nematodes at the time of planting of the second crop compared to the levels following plantings of susceptible varieties.
A 2004 study looked at the level of nematode RKN damage on cucumber and squash crops planted following RKN susceptible and resistant varieties of bell peppers in a double crop system.4 RKN gall formation and reproduction (number of eggs per gram of root tissue) were significantly lower on the RKN resistant pepper than the susceptible variety. In the following cucumber and squash crops, the level of RKN galling on roots was significantly lower, and the yields were significantly higher (87 and 55%, respectively) on the cucumber and squash plants grown following the resistant pepper variety compared to the levels on plants grown following the susceptible variety (Table 1). In a 1998 study, where RKN susceptible bell pepper varieties were grown following RKN-resistant and susceptible varieties of cayenne peppers, the peppers grown in plots previously planted to the resistant cayenne variety showed lower levels of root galling and higher yields than the peppers grown following the susceptible cayenne variety.5
Similar studies evaluating the effect of planting RKN-resistant and susceptible tomato varieties followed by cucurbits in double-crop systems have also found lower levels of RKN root damage and higher yields on the crops planted after the resistant tomato varieties. In a 1998 study on a tomato/cucumber double-crop system, cucumbers were planted after a tomato variety with RKN resistance and an RKN susceptible variety.6 The RKN soil population at the end of tomato harvest was higher in the susceptible variety plots than in the resistant variety plots. In the following cucumber crop, the root-gall ratings were higher on the plants in the former susceptible tomato plots compared to the plants grown in the former resistant tomato plots. Both premium and total marketable yield levels were higher on the cucumber plants grown in the former resistant tomato plots than on the plants grown in the former susceptible tomato plots. Other studies looking at tomato/cucumber and tomato/melon systems reported similar results in terms of lower root galling and higher yields in the cucurbit second crops following RKNresistant tomato first crops.7,8

SOURCES
1Desaeger, J. A., and Csinos, A. S. 2006. Root-knot nematode management in doublecropped plasticulture vegetables. Journal of Nematology, 38:59–67.
2Desaeger, J. A., & Bui, H. X. 2022. Root-knot nematode damage to a cucurbit double crop is increased by chloropicrin fumigation on the previous tomato crop. Pest Management Science, 78:4072–4082.
3Noling, J. 2019. Nematode management in tomatoes, peppers, and eggplant. UF IFAS Extension. ENY-032.
4Thies, J. A., Davis, R. F., Mueller, J. D., Fery, R. L., Langston, D. B., and Miller, G. 2004. Double-cropping cucumbers and squash after resistant bell pepper for root-knot nematode management. Plant Disease 88:589–593.
5Thies, J. A., Mueller, J. D., and Fery, R. L. 1998. Use of a resistant pepper as a rotational crop to manage southern root-knot nematode. HortScience 33:716-718.
6Colyer, P. D., Kirkpatrick, T. L, Vernon, P. R., Barham, J. D., and Bateman, R. J. 1998. Reducing Meloidogyne incognita injury to cucumber in a tomato-cucumber double-cropping system. Journal of Nematol. 30:226-231.
7Hanna, H. Y. 2000. Double-cropping muskmelons with nematode-resistant tomatoes increases yield, but mulch color has no effect. HortScience 35:1213-1214.
8Hanna, H. Y., Colyer, P. D., Kirkpatrick, T. L., Romaine, D. J., and Vernon, P. R. 1994. Feasibility of improving cucumber yield without chemical control in soils susceptible to nematode build-up. HortScience 29:1136-1138.
ADDITIONAL INFORMATION
For additional agronomic information, please contact your local seed representative. Performance may vary, from location to location and from year to year, as local growing, soil and environmental conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on their growing environment. The recommendations in this article are based upon information obtained from the cited sources and should be used as a quick reference for information about vegetable production. The content of this article should not be substituted for the professional opinion of a producer, grower, agronomist, pathologist and similar professional dealing with vegetable crops.
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5011_441950 Published 08/20/2024