Protect Stored Beans from Weevils

Backgrounder

Today we are going to talk about a couple of ways you can prevent bean weevils from damaging stored beans.  We will talk about adding ashes or vegetable oil to the beans in storage.

The very first step is to determine whether or not it is even necessary to use pest control.  In other words, you need to decide whether or not there are enough weevils in the stored beans to make it worth your while to control them.  To find out, separate several handfuls of beans from the rest of the beans.  From this batch of one pound, count out 100 beans.  Look for tiny, round holes about 2 millimetres across made by the weevil larvae.  Repeat this process several times.  If 4 out of every 100 beans that you count have these little holes in them, you will have to use some kind of control.  Less damage than this, that is, less than 4% damage, will not cause a significant reduction in germination, food quality, or market price.

Once you decide there is enough damage so that you need to control the weevils, here is what you can do.

Between beans there are spaces where the weevils move around.  If you fill these spaces with fine, dry ashes (the finer the better) it will be more difficult for the weevils to survive.  Mix 1 part ashes for every 5 parts of grain.  In other words, if you are storing 5 kilograms of grain, then you add one kilogram of ashes.  Insects trying to move between the beans will scrape or cut their bodies on the ashes.  Through the cuts they will lose moisture, get dehydrated, and die.

Some people in Guatemala also use dried ground chillies.  They add one per cent chillies to the stored grain.  In other words, they add 10 grams of dried ground chillies to 1 kilogram of grain.  This works well if chillies are easy and inexpensive for you to get.  Remember that the materials you use, ashes or chillies, should be very fine and very dry.

Vegetable oil can also be used to protect stored beans from weevils.  The oil blocks the insects’ breathing pores so they cannot breathe.  Then they die.

Add 50 millilitres of vegetable oil to 11 kilograms of dried beans.  Mix well and store in a cool place.  If you do not have much oil, you can use half water and half oil.  If you are going to use this method with beans for planting, you must be very careful not to use more than 50 millilitres for every 11 kilograms of beans.  Otherwise the oil can also damage the pores of the beans and they will not be good for seed.