Soja

"Trips" insects in soy fields
Rubén A. Massaro, Agricultural Engineer. EEA Oliveros

The reason for the dry periods in the Pampa region has been without a doubt, the manifestation of elevated quantities of the insect known as "trips". In the north of Buenos Aires, center and north of Santa Fe and all of Entre Rios, the rains usually are not enough to minimize its presence.
These small FITOFAGOS (0.5 to 0.8 mm in length) have been present in the crop for lots of years, and besides being a potential plague, they constituted the food source for beneficial species like the Orius (Chinche Pirata) and Geocoris (chinche ojuda). During the last 20 years, only in a few cases they’ve reach damage levels that made us think of using insecticide.
During the 96/97 campaign the presence of the species Caliothrips Phaseoli in soy crops, have been registered. During the 89/90 period, soy crops infected during the first states of development we replaced in the localities of Oliveros, Coronel Arnold and Villa Mugueta (Santa Fe). The species identified then were Thrips tabaci and Frankliniella Schultzei.

"Trips" present in the last agricultural cycle were Caliothrips phaseoli (identified in different areas of Santa Fe and Entre Rios) commonly referred to as "beans trips".

"Trips" are the cause of 3 different types of damage:

  1. Direct damage, (breaking the superficial cells and sucking the juices). Then, small white spots appear (empty cells) that later turn yellow, brown and even red. The leaves look silver or gray and then a yellowish red. This damage increases water loss in plants and, in dry soil conditions, they dehydrate and die even more so. With high quantities of "trips" per leaf (40-50), these can age prematurely and drop from the plant.

  2. The wounds in the leaf could be a way in for illnesses (fungi, viruses, bacteria).

  3. Transmission of viruses that affect soy. This has not been registered in studies done during the 89/9- campaign.

    Insecticide control decisions

    To decide on insecticide treatments, some important aspects related to the "trips" have to be considered:

  • The quantity of trips needed to require insecticide is high: more than 50 per leaf.

  • Although we can achieve a high mortality rate with the treatment of insecticide, re-infestation (the re-appearance of the plague) is very fast because the adults emerge from the ground, where the nymphs from the last stage are. This can happened in 5-7 days with adults and 15 days for birth of new nymphs. This is proof that insecticides have a low persistence in crops.

  • In crops that have surpassed the grain’s maximum volume (R6-MV), there are just a few days left for the normal drop of the leaves (state R7), so the aging and drop of the leafs due to insecticide will have a minimum effect or no effect what so ever on the crops performance. It is, however, very important to try and preserve the leaves in crops that are about the reach or are in the grain giving stage (R5 and R6).

  • Rains will not make the trips disappear quickly, but their number should start dropping during the next few weeks. The plants, however, will manifest a recuperation due to sufficient water to compensate the loses due to the wounds.

  • There are no registered chemical insecticides for "trips" in soy farming. There are, however, for other crops like cotton and horticulture.

  • Insecticide control requires reaching the lower leaves because the adults move into them and the population grows from there up (this is where we find the highest number of them and these are the leaves that drop first).
    This means that an excellent application is require.

 

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