Controlling sucking pests and preserving natural enemies in cotton

Cotton cultivation in the Brazilian Cerrados requires a lot of effort to avoid losses caused by the occurrence of pests. A group of insects that has caused significant losses is the suckers, which cause direct or indirect damage to plants. Aphids, whiteflies, thrips, mites and stink bugs can weaken and even kill cotton plants by sucking the sap or transmitting viruses, or compromising their production by directly attacking the floral structures or contaminating the plume.

Aphids

The cotton aphid (Aphis gossypii) is one of the first pests that occur in cotton and can be detected soon after the plants germinate. This polyphagous insect lives on several plant species, including wild plants, from where it migrates to cotton plants in the initial stage of vegetative development. Once in the cotton crop, when at low population density, the aphid is an important bioindicator. As it serves as food for several natural enemies, its presence in low quantities indicates the possibility of maintaining beneficial species, which control it and control other important crop pests. When in high population density, it causes injuries to the plant due to the continuous suction of sap and compromising the photosynthesis process, or compromises the plume when its excretion falls on it, forming caramelized cotton.

White fly

Whitefly populations (Bemisia tabaci biotype b) are observed in cotton crops mainly due to the migration of these insects from neighboring senescent crops, such as beans and soybeans. Although it is not the insect's preferred host, the cotton plant receives these populations which, when in high density, cause severe injuries. During the feeding process on cotton leaves, the whitefly injects toxins with its saliva, which cause deformation, growth arrest and a decrease in the capacity to produce reproductive structures.

Gut

Thrip infestations (Frankliniella schultzei) are observed at the beginning of cotton cultivation, shortly after emergence or, more rarely, after the beginning of the plants' reproductive phase. These insects compromise the development of new plants, causing oversprouting due to the breakdown of apical dominance. Its occurrence in later stages of the crop, after flowering, does not usually cause problems, since the insect remains in the flowers of the plants, without compromising development or production.

Mites

Mites (Tetranycus urticae e Polyphagotarsonemus latus) initially occur in reboleiras but their dispersion is facilitated by the wind and the application of some insecticides, such as those from the pyrethroid group, as they encourage movement. Its attacks shorten the plants' cycle, as well as compromising their productive capacity, the apples have abnormal development and the fiber's quality is compromised. The most common species are the two-spotted mite and the white mite.

Bedbugs

The most important species of sucking bug in cotton crops and which usually comes from soybean crops is the brown stink bug (Euschistus heros). These insects cause damage to flower buds and apples, causing deformation, stunting and abscission. Attention should be paid to the fact that both phytophagous and predatory stink bugs occur in cotton cultivation. Predatory bed bugs control several pests, especially caterpillars. Morphologically, phytophagous bugs differ from predators in their mouthparts: while phytophagous bugs have a thin and long rostrum (“beak”), extending to the second pair of legs; predators have a curved and short face, which does not exceed the first pair of legs.

Injuries caused by suckers

The continuous sucking of sap by aphids, whiteflies and thrips causes various types of injuries, such as leaf deformation, abnormal plant development, impaired photosynthesis and compromised fiber quality due to contamination by their excrement. Bed bugs suck the apples, causing their deformation and the “parrot beak” effect, which prevents them from opening normally and harvesting the fiber. Mites cause necrosis and leaf fall, compromising photosynthesis production and plant development.

Sucker control measures

• Climate control: Climatic factors can favor the development of suckers or, on the contrary, exert natural physical control over their populations. Cloudy, hot and humid weather favors the development and reproduction of white mites. Summers favor the occurrence of spider mites. Periods of high temperature and low humidity are also conducive to increased thrips populations. On the other hand, heavy rains reduce the population level of sucking insects in general, due to the physical control of the drops on the insects.

• Chemical control: The use of broad-spectrum insecticides or acaricides often leads to an increase in the number of applications during the harvest, due to the elimination of natural enemies. The producer should preferably opt, for this reason, for selective products. Systemic insecticides applied to seed treatment are less harmful to natural enemies. Seed treatment protects cotton seedlings for up to 30 days after germination. If the attack occurs after the end of the residual period of seed treatment, the use of systemic insecticides, such as neonicotinoids, and translaminar insecticides, such as spinosyns, via aerial spraying, will be indicated. Growth-regulating insecticides such as buprofezin and pyriproxyfen are also selective to natural enemies and lethal to young forms of suckers.

• Varietal control: A control method with great ecological advantage in the management of aphids, the use of resistant varieties preserves the populations of natural enemies present in the crop. This occurs because the levels of control adopted may be less rigorous in resistant varieties than in susceptible ones, allowing the concomitant action of natural enemies that prey on or parasitize aphids and other crop pests. Aphids transmit the vein mosaic virus, which causes blue disease. Varieties resistant to the virus, even if infected, do not develop the disease.

• Cultural control: the elimination of host weed plants, volunteer plants or cotton ratoon, reduces the initial foci of suckers, as it suppresses the individuals that would complete development on these alternative foods. The destruction of ratoon plants after harvest helps decisively in suppressing sucker infestations at the end of the cotton cycle, which will have a positive impact on subsequent harvests of summer crops.

• Biological control: Among the natural enemies of sucking pests, there are several species of predators, parasitoids and entomopathogenic microorganisms. Some are naturally occurring and need to be conserved in agricultural environments; others are released by flooding (large numbers of individuals at once to quickly reduce the pest, with no expectation of continuous effect); others released by inoculation (small number of individuals, released one or more times, with the intention of multiplying in the environment).

Parasitoids of eggs, larvae or nymphs are specific biological control agents for each target pest. Inundative releases of parasitoids contribute greatly to the reduction of sucker populations. Predators such as species microwasps Lysiphlebus testaceipes, Aphelinus gossypii e encarsia formosa, among others, control suckers.

Predatory insects are generalists, which makes it easier to maintain them in the agricultural area, since, in the absence of a host, they look for others. The most common species are bed bugs geocoris sp. It is Orius insidiosus, ladybugs Cycloneda sanguinea e coleomegilla maculata, the garbage man Chrysoperla externa, and the wasp Polistes versicolor.

Entomopathogenic fungi cause infection due to the germination of their spores when penetrated into the insect's cuticle. Among the entomopathogenic fungi, the species that stand out in the control of suckers Metarhikum anisopliae, cordyceps javanica, beauveria bassiana e Paecilomyces fumosoroseus. Products based on entomopathogenic fungi registered for the control of suckers are already available on the Brazilian market.

Decision-making

Although the occurrence of sucking insects in cotton crops is common, these insects only cause damage when they reach the level of economic damage. Constant sampling of their populations in the field and the presence of their natural enemies, observation of the climate and possible causes of migration (neighboring crops in senescence or nearby host plants) are decisive factors for good decision-making. The combination of the various control methods mentioned and action at the most appropriate time are essential for efficient control of sucking pest populations.

By José Ednilson Miranda, Bruna Diniz Mendes Tripode, Valeria da Silva Jardim e Ana Mônica Teixeira Saraiva, Embrapa Cotton

Article published in issue 291 of Cultivar Grandes Culturas Magazine