"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 theyve 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:
-
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.
-
The wounds in the leaf could be a way in for illnesses (fungi, viruses,
bacteria). -
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 grains 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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