Infestation levels in stored grains
Technical note on infestation levels in stored grains, with a focus on diagnosis, prevention and criteria applicable to professional pest management.
This is a topic that is not normally discussed frequently, however it is necessary to consider it and define more precisely what the problem generated by insect pests is in each installation. We know that weevils, woodworms, borers, popcorns, moths, etc. They are all of subtropical origin and are today found in cereal bulks around the world. In other areas of plant therapy we can hear talk of damage threshold, pest management, for example of so many caterpillars per m2. In the post-harvest this is not the case. The costs involved with control are low enough, compared to the potential damages, to which is added the difficulty of knowing what is happening.
THE TRUE IS THAT PESTS, DUE TO THEIR CAPACITY OF ADAPTATION AND UBIQUITY, AND THEIR GREAT POWER OF MULTIPLICATION, CONSUME, DAMAGE AND CONTAMINATE OUR GRAINS with an infestation of an entire bulk. It is common to hear about dry heating sources caused by insects, meaning that it is very possible that in a 1000Tn bulk we have only 150Tn with a significant insect attack. Unfortunately, in many countries in the southern cone, prub-traps (insect traps) are not available and the use of monitoring systems is very limited, which is why we lose sensitivity in detection and we only see the insects when they have already advanced significantly.
Years ago, to give some idea about the risk in storage, we defined 1 weevil per kg or 2 woodworms per kg as dangerous. If we make an estimate in a 1000Tn silo we would have 1 million weevils, approximately half of them are female and in 30 days we can have 50,000,000
of offspring in F1, that is, 50 insects per kg. As we see, with temperatures higher than 25ºC, we cannot be careless, in a few weeks we could have unpleasant surprises. To help define the severity of the infestation we propose to consider the following 5 degree scale:
STORED GRAINS
Grade 0: No insects are seen in the facilities or in the bulk, several crops without development of pest attack. (Of course you cannot prevent pests from entering the grains secretly, however with physical and chemical control you can prevent them from developing). Grade 1: Presence of insects in the facilities, it is possible to find them alive
cation – etc.) allows us to better interpret the reality of the silo plant. In any case, the use of this type of scale cannot by itself overcome the lack of sensitivity in pest detection. Let us keep in mind that by definition, in pest control, we want grain free of live and dead insects, with low cost, free of
LET'S REMEMBER THAT THE VAST MAJORITY OF INSECTS PESTS OF STORED GRAIN ARE NIGHT FLYERS or dead, among the waste, on the walls, foot of the wheel, brakes, aerations, flying over the bulk, etc. Grade 2: Presence of insects in the facilities and in some bulk that has been stored for more than 4 months, sporadically. Grade 3: Consecutive infestations campaign after campaign. Inability to avoid typical damage from pests such as grain chopping. Grade 4: Widespread infestation, weight and quality losses due to pest attack, truck rejections. If we put this or some other type of scale to use, we will be able to better understand the situation of each plant that handles grains/seeds. This information added to the description of the work carried out (pesticides used – sampling systems – forms of hazardous waste and in a safety framework. To improve detection, there is already available technology, we can recommend 3 of them: 1) Moving grain sampler: Various systems that allow moving grain samples to be taken mechanically have been known for several years. So that important samples can be taken, without depending on labor and thus have more representative samples. Let us keep in mind that issues such as mycotoxins require more intense sampling, so this type of equipment is more essential. 2) Traps: There are those that require pheromones and others that can work without them. The most recommended WE CAN'T GET USED TO LIVING WITH PESTS, THEY CONSUME, POLLUTE, PROMOTE WARMING, HELP MULTIPLY FUNGI, IN DEFINITELY THEY REMOVE NUTRITIONAL AND ECONOMIC VALUE FROM OUR GRAINS is the prub-trap, homemade traps can also be used, strategically located to detect insects. 3) Mechanical screens: Several years ago we promoted the use of this type of equipment, which is already present throughout the world. The manual screen that is normally used to see insects is designed to work with just a few grams, and it always depends on the operator. Mechanical screens can work several kilograms per minute, without taking the operator's time and therefore being more sensitive when detecting insects. We do not have practically available equipment that allows us to detect hidden infestations. In this work of defining infestation levels, it is essential to have a good knowledge of pests, their biology, how to differentiate them, etc. For example, it is still common for plant people to confuse the borer (Ryzopertha dominica F.) with the woodworm (secondary infestation insects), since for many it is only the weevils of the genus Sitophilus, those with the pointed mouthparts, that can be considered primary infestation insects. However, the borer is capable of chopping many grains throughout its life, while the weevil of the genus Sitophilus only chops one. If we have pest problems we cannot think about continuing doing the same as we have done until now, since the problems will only grow. On the other hand, in addition to the cost that must always be tried to lower, there is the problem of waste and resistance. Today we have the technology for every type of situation, so that pest damage is a thing of the past.