Corn is an extremely versatile crop, which is why it occupies large areas of Brazil. The main advantages of the crop are: 1) its grains are used for various purposes; 2) it is an easily commercialized product; 3) there are hundreds of cultivars and hybrids available. Furthermore, corn is resistant to some of the main species of phytonematodes that occur in Brazil: Heterodera glycines, Rotylenchulus reniformis, Meloidogyne hapla e Ditylenchus dipsaci. Therefore, corn is extremely valuable as a rotation or succession crop for controlling these four species. As the other side of the coin, it is susceptible to four other species of great importance: Pratylenchus brachyurus, P. zeae, P. jaehnie Meloidogyne incognita. To complete the scenario, it is known that several hybrids (20%-30% of the total) are resistant to Meloidogyne javanica.
In Brazil, the nematodes that cause the most losses to soybeans are Heterodera glycines, Pratylenchus brachyurus, Meloidogyne javanica, M. unknown e Rotylenchulus reniformis. From a purely nematological point of view, corn can be used without restrictions to control soybean cyst nematode (H.wisteria), as all cultivars and hybrids are resistant, causing a population reduction of this nematode. By the way, every soybean farmer knows that rotation or succession with corn is an effective method of controlling H. wisteria. The same recommendation is valid for the reniform nematode (R. reniformis), whose importance is still small, but growing for soybeans.
The basis of control H. wisteria e R. reniformis in soybeans has been the use of resistant cultivars. However, rotation or succession with corn are also measures of great value, as alternatives or complements to resistant cultivars: in the first case, when the available resistant cultivars are not suitable for the location, in the second, when an additive effect is desired.
Before the detection of cyst nematode in Brazil, in
However, it is necessary to ensure the identity of the species of Meloidogyne. Less frequently, another species of root-knot nematode occurs in soybeans: M. unknown. In Brazil, there are no corn hybrids resistant or moderately resistant to M. unknown. Therefore, if the species Meloidogyne present for M. unknown, corn will cause a large increase in its density and, as a consequence, in soybean losses.
There are no corn hybrids resistant to P. brachyurus, however, there are some with moderate resistance (FR between 1 and 5). Several farmers use soybean-corn succession in areas infested with P. brachyurus, but they must be aware of the risk of losses in soybeans, which should only be accepted if the income perspective provided by corn is really very positive. It is also necessary to take into account the density of P. brachyurus (the risk is greater from values greater than 200 specimens per 200cm3 soil) and the degree of resistance of the corn to the nematode (susceptible or moderately resistant).
Corn in succession with beans
The nematodes that occur in bean crops are the same as those in soybeans, therefore, the recommendations when using corn as a rotation crop are the same as those listed for soybeans. However, there are differences in the importance of nematode species. In common beans, the species that cause the greatest losses are M. javanica e M. unknown.
Corn in rotation or succession with cotton
In Brazil, the nematodes that cause the most losses to cotton are M. unknown e R. reniformis. Considering that corn is susceptible to the first species and resistant to the second, it should not be used in rotation or succession with cotton in places infested by M. unknown, but it is highly recommended in the control of R. reniformis. In the case of mixed infestations, the decision to use corn should be made based on the density of M. unknown, as it is the species with the greatest potential to cause losses to cotton. If the density of M. unknown is greater than 100 specimens per 200cm3 of soil, this rule is sacred: do not use corn under any circumstances. Losses in the range of 30% to 50% can be expected if this rule is not respected.
Another species worth highlighting is P. brachyurus, which is very common in the country’s cotton fields. Fortunately, cases in which it causes losses in cotton are rare.
Corn in succession with potatoes
The main potato nematodes in Brazil are, in decreasing order of importance, M. javanica, M. unknown e P. brachyurus. It is therefore worth the rule that, in areas infested by M. javanica, use resistant hybrids or cultivars; in areas infested by M. unknown ou P. brachyurus, do not use corn under any circumstances. Another situation is mixed infestation by two or three species of nematodes, a situation in which, for safety reasons, corn should not be used.
Corn in succession with lettuce, beetroot and carrot
The most harmful nematodes to lettuce, beetroot and carrots in Brazil are M. javanica e M. unknown. The use of corn poses a great risk of losses for the three vegetable crops in places infested by M. unknown, and at moderate risk in places infested by M. javanica. Both species cause equal losses for the three vegetable crops, however, succession with corn is less dangerous in places with M. javanica, as corn hybrids are, for the most part, resistant (around 20%-30% of them) or moderately resistant. For this reason, identification of the root-knot nematode species is very important.
In some regions, such as Moji das Cruzes, identification has an even more significant value. In this important vegetable producing area, in addition to M. javanica e M. unknown, another very common species is M. hap. All corn hybrids are resistant to this species, therefore, the role of this grass is completely different from the scenario with M. unknown ou M. javanica: it is highly recommended in succession with lettuce, beetroot and carrots, to control M. hap.
Corn in succession with garlic and onion
The most important nematode for garlic and onion is Ditylenchus dipsaci (stem and bulb nematode), in all the main producing regions of Brazil (Santa Catarina plateau, Alto Paranaíba valley, among others). Corn is susceptible to some breeds of D. dipsacci, but is resistant to those currently occurring in Brazil. Therefore, at least for now, corn is a valid crop for succession with garlic and onions, in places infested by D. dipsacci. However, nematodes M. javanica e M. unknown also cause losses to the onion.
Corn as an intercrop in coffee plantations
In coffee plantations, intercrops bring several benefits, notably protecting the soil against erosion and desiccation and increasing the supply of nutrients. If the intercrop has economic value, the income provided to the farmer is added to the list. However, for the purposes of this publication, it is important to know the effect of corn on nematodes that occur in coffee plantations. Among the nematodes harmful to coffee plants, corn is resistant to Meloidogyne exigua, M. paranaensis e M. coffee, but susceptible to M. unknown, Pratylenchus jaehni e P. brachyurus.
Final considerations
In conclusion, corn can be a highly valuable tool in controlling phytoparasitic nematodes, as long as the farmer has three essential pieces of information: 1) the nematodes that occur in his area; 2) nematodes that cause losses to the crop that will be planted in the area; 3) the resistance of corn to nematodes that occur in the area and that cause losses to the crop to be planted.
Click here to read the article in Revista Cultivar Grandes Culturas, issue 175.
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