Scouting is the foundation of a successful IPM system

March 2019

Written by a retired farmer

Scouting really means walking through your lands and inspecting whichever crop is relevant within an Integrated Pest Management (IPM) system from pre-planting to harvesting and beyond for some important aspects of whole production management cycle.

IPM systems
Once a farmer has decided to implement a strategy to start an IPM system it is important to keep a record of what is to be monitored and recorded.

The actual situation prevailing in the crop aspects to be checked can then be compared to the targeted outcomes and crop planning that should have taken place after the last crop when developing the total farm budget or gross margin analysis.

Mistakes made in the previous seasons can then be corrected in the current season.

What are we looking for?
At planting, the soil conditions will affect germination percentage which in turn can be reduced by a spectrum of pests even before emergence. Count and note what plant population emerged. Compare this to your planned target and every few days inspect the roots, emerging leaves or stems and see if there are any signs of worm or beetle damage.

The monitoring within the IPM system will enable you to know from the early growth stages and throughout the various growth stages to maturity when the potential damage from an identified pest on the crop makes it economically feasible to use chemical control.

Sometimes after an early observation of pest damage, preparations can be made to spray the crop as and when it is determined that stem, leaf or young cob development damage has reached the economic threshold to make spraying mandatory. The cost of spraying for that pest must be more than covered as the crop recovers the ability and possibility of achieving economically viable yields. If left, the crop will fail. Your chemical supply consultant as well as your seed supplier should always be consulted as soon as you notice a pest infestation as to the best time or stage to implement chemical control.

The choice of the many maize cultivars to plant that are resistant to pests (Bt Maize) and diseases is the most critical decision to make from the start.

It is required of the farmer, especially if this is your first season of planting maize, to read about the subject or attend relevant courses so that you are familiar with the wide spectrum of insects and weeds that can influence your maize crop at any stage.

If you don’t know what to look for you will almost always be too late to save you crop by the time you realise there is a problem. The farmer must also know the signs of initial infections of fungus and other diseases as well. You must know what part of your young growing should be inspected for damage or stalk borer eggs or young caterpillar leaf damage.

If you find a damaged plant, leaf or cob keep a sample in a bag or bottle so that the actual pest can be identified by an expert. In some years infestations from an unfamiliar insect can occur catching the farmer and consultants off-guard.

Remember that while scouting you are also observing crop growth and health, the presence of pests as well as the emergence and development of any undesirable weeds that need to be chemically or mechanically controlled.

Heat units
Heat units or day degrees are a measure of time and temperature determined by the amount of time the sun is shining and the prevailing day and night temperatures. The amount of sun energy available for photosynthesis with regards to the crop growth coupled with the temperatures experienced will influence the speed at which the crop reaches various benchmark growth stages.

Depending on planting date and the prevailing temperatures being experienced in a particular season those benchmarks can be different from the normal standards expected. Many of the main seed suppliers have a wealth of information that show the growth stages of maize in great detail and can be downloaded from their websites. The farmer must be familiar with these so that he can communicate the growth stages to his seed and/or chemical supplier so that he can always optimise the timing and quantity of the chemical control to be used.

Just as the heat units affect the growth of the crop so they influence the physiological activity and growth cycles of insects that could become pests in your crops. An insect’s temperature is thus similar to the surrounding environment. The climatic cycles will thus affect when stalk borer moths, for example, begin flying for the first cycle and laying eggs on your young maize plants. This in turn determines the timing after one cycle of the young borer caterpillars’ growing into flying moths the timing of a second infestation in the maize crop.

This season’s IPM strategy
Each maize cultivar will have an expected relative number of days to 50% tassel and physiological maturity. Depending on your farming area and climate the point of 50% tassel could be reached from 64 to 84 days after planting and physiological maturity from 105 to 240 days after planting. Know these benchmarks for the cultivars you have planted.

The early rains expected might have come late in your area, so planting might have been delayed. Maize planted on 15 November 2018 could only be at 50% tasselling towards the end of February 2019. It would have been important to intensively scout for the second cycle of stalk borer eggs or evidence of leaf damage by young caterpillars over the whole month of February.

For the later plantings any potential damage to the developing maize cobs should be checked with regular inspection of the cobs. The earlier periods of scouting would have helped to spray and control early infestations of stalk borer to avoid any damage to the cobs later. Constant monitoring of the crop by scouting should be done until the crop is harvested. It might be possible during April, while scouting, to look at possible yield estimations using the number of pollinated kernels forming in the developing cobs.

Publication: March 2019

Section: Pula/Imvula