Pests also like potatoes

Potato crops are inhabited by a large number of insect species. The diversity and quantity vary from region to region, due to the method of cultivation, cultivars, climate, etc. In southern Brazil, although several species of pests are found, the relative quantity is, in general, small. Pests that are extremely serious and limiting in other conditions, such as the Potato Moth and the Mining Fly, are still not present in that region.

Direct damage from potato pests occurs when they feed: a) on the leaves (leaflets), with a reduction in the photosynthetic area; b) in the roots and stolons, with a reduction in the production area; c) in tubers, with a reduction in qualitative and quantitative production. Indirect damage is due to the transmission and predisposition of the plant to the incidence of viral, bacterial and fungal diseases.

The main pests of the aerial part are Diabrotica, Burrinho, Flea, Moth, Aphids, Whitefly, Mining Fly and Mites. These are generally local problems and, under certain conditions, whether due to the climate, the cultivar, or the planting system, they constitute a factor in the economic reduction of production. Therefore, widespread use of control measures (insecticides) cannot be considered. There is no doubt that decision-making to control aerial pests using insecticides must be based on observation and monitoring of the crop.

Although the economic levels and, consequently, the levels of control for pests in the aerial part of potatoes have not been determined, at least the observation and extent of their presence in the crop area must be the determinants for decision-making and action to be taken. control.

Soil pests

The main pests that attack the root system (roots, stolons and tubers) of potatoes are potato larvae (

,

spp), the flea (Epitrix spp), the wireworm (

spp), the screwworm (

spp), the coró (

spp,

), in addition to root-knot nematodes (

spp).

The damage caused by soil pests is generally a loss of quality in the appearance of the tuber, although when it occurs prematurely in the stolons and tubers, it adds up to a considerable reduction in production.

In general, the potato market is increasingly demanding regarding the appearance of the product, including the almost total absence of holes and other lesions on the tuber. Currently, the producer has to resort to the use of insecticides that protect the plant's underground system to minimize the chances of attack and damage to the tuber. Other techniques for controlling underground pests, although studied, are not yet widely used. Below we address the two main potato soil pests, with a summary of experimental results with soil insecticides carried out at Embrapa Clima Temperado.

Kitty at the parade

The adults of Vaquinha, the

(Coleoptera: Chrysomelidae), are beetles with an oval body, green color, six yellow spots on the wings, three on each side. An extremely polyphagous pest, it attacks more than 30 crops, including beans, corn, pumpkin, watermelon, melon, cucumber, tomato and fruit trees, among others. It is active throughout the year and its quantity will depend on the presence of the host and temperature. The population increases from August onwards and decreases after May, in southern Brazil, for example.

The life cycle is long and depends on the host where it develops. For potatoes, it takes about 40 days for spring planting and 50 days for autumn planting. It develops several annual generations, on a single or multiple hosts. There may be up to two in potatoes in the spring cycle and one or two incompletes in the autumn cycle.

Adults only attack the foliage, consuming the leaflets. The economic damage this could cause to potato cultivars is not yet known. It is known, however, that when the attack by kitty adults occurs at the beginning of the plant's development cycle, the probable loss is small, but if it happens in the middle of the cycle, there may be a reduction in production, having no influence on the final phase. of the cycle.

Its larvae have an elongated body, creamy-white in color, with hair, a black head and a black plate at the posterior end. The larvae attack and cause damage only to potato stolons and tubers. The stolons are the organs responsible for the formation of the tuber. The cowpea larva attacks the tip of the stolon, preventing the tubercle from forming. It is true that certain cultivars (e.g. Macaca) have a greater quantity of stolons emitted, which can compensate for the formation of tubers in the plant.

There are experimental data that demonstrate the influence of planting previous crops in the potato planting area. The crops that reduced the incidence of tuber attack were garlic, onion and corn, when compared to beans, soybeans, potatoes and fallow crops. There is no convincing data to support the need to destroy cultural remains of any previously planted crop or of the potato itself. However, whenever possible, cultural remains should be incorporated in the best way possible.

Wireworm is also a pest

The adults of Bicho Arame (

spp.) are beetles with an elongated and flat body, color varying from brown to dark brown. The characteristic of these beetles is that they can jump and return to their normal position when placed on their back. The larvae have a typical shape, an elongated and flat body, orange-brown in color and a shiny, glassy appearance.

Wireworms are polyphagous, attacking numerous crops, such as sweet potatoes, carrots, beets and other crops and spontaneous plants that remain or are in the soil. The life cycle of these insects is long. The larvae take about three months to fully develop.

Adults are very active at night. During the day, they take refuge under part of the plants and in cracks in the ground, for example. Consequently, mating and laying occur during the night. The eggs are laid in cavities in the ground, under plant debris or in cracks in the ground. Most eggs are laid in groups.

The larvae attack potato tubers, causing round, deep holes.

Larvae develop best in soils with high humidity. When the soil is too dry, they look for the tuber more, causing greater damage. Therefore, in harvests with drought and periods of drought, the damage from wireworms may be greater. Soil temperature is another important factor, influencing the vertical distribution of wire larvae. The hotter it is, the deeper the larvae will be, attacking the tubers in this position.

The wireworm attack is not uniform across the crop area, but in patches where there are more favorable conditions for development. Humidity is believed to be more decisive.

Controlling pests

Controlling these two pests with soil insecticides has been the most used and efficient way at the moment. There are few products available on the Brazilian market recommended for this purpose. Some products provide more constant and better results, depending on local conditions.

Another important variable was the planting season. In the spring harvest, insecticides provided better protection for the tubers than in the autumn harvest, as shown in table 2.

Recently, we developed an experiment where commercial products available on the market and recommended dosages for use in the soil in potato cultivation were evaluated. The intention was to jointly and comparatively evaluate all these products, providing producers with the possibility of better evaluating the performance of the insecticide of their choice in potato farming.

The potato producer undoubtedly has product choice options available, given that the majority provided more than 75% control of these two pests. It is important to emphasize, once again, that the analysis of these results was based on the level of seven average holes per potato tuber (tuber retained in the 5,0 x 5,0 cm sieve). If the potato destination market is more demanding in appearance, these results may have reservations.

José Antônio Salles

Embrapa Temperate Climate