Whilst the presence of weeds strongly influences the pest standing of cutworm, the affect of soil moisture on elements similar to their biology and behavior are continuously lost sight of. Entomologist and Bt-maize professional Prof Johnnie van den Berg and Zunel van Eeden, a grasp’s pupil at North-West College’s Built-in Pest Control workforce, have undertaken analysis on cutworm behaviour, keep an eye on and insecticide resistance.
Picture: Provided
The average cutworm, Agrotis segetum (Lepidoptera: Noctuidae) is a harmful pest of maize, particularly within the Highveld area of South Africa. Over the 3 earlier cropping seasons, many reviews of keep an eye on failure had been made all through the area.
Even though there may be hypothesis relating to insect resistance to pesticides, the seen keep an eye on disasters are in all probability because of different elements, similar to larval behaviour and environmental prerequisites, and, significantly the presence of weeds.
Why is it tricky to spot cutworm?
Id of cutworm because the pest accountable for harm to seedlings in a specific land is hard because of their dependancy of tunnelling into the soil right through the day and feeding at evening.
It’s due to this fact tricky to stumble on larvae to go along with the seen injury signs, which might be able to even be because of different soil insect pests.
When broken or lifeless seedlings are seen, the soil across the base of the vegetation will have to be tested for the presence of cutworms. Larvae will also be seen underneath clods, within their tunnels, or in soil cracks.
Indicators of cutworm infestation
Cutworm injury is influenced by way of the amount and measurement of larvae found in lands. Provided that seedlings are significantly broken and when stand loss happens, can injury be thought to be economically essential.
Injury signs to maize seedlings will also be grouped into 5 classes, relying at the measurement of the larvae and the age of the plant.
In row plants similar to cotton, maize and sorghum, lack of plant stand is continuously the primary symptom that cutworms is also found in a box. A unmarried larva might sever a number of seedlings and can continuously reduce one plant and transfer directly to the following.
In circumstances the place cutworm infestations are serious, it would even seem as though probably the most rows have disappeared as early as 4 days after seedling emergence. In those circumstances, it can be vital for manufacturers to replant.
- Small holes in furl leaves of seedlings
When moths lay their eggs on or underneath younger seedlings, the L1 and L2 larvae that hatch from those eggs expand and feed at the furl leaves of the seedlings. Foliar feeding will also be observed as early indicators of cutworm infestations.
The kind of feeding will also be prominent from different maize pest injury as shot-hole-like holes that seem at the leaves of seedlings.
The feeding development of cutworm larvae alternate from the 3rd instar (segment between two classes of moulting) and so they now have a damaging response to gentle and so they cover underneath floor right through the day.
Larvae emerge from the bottom at evening and transfer from plant to plant, severing younger seedlings simply above or at a brief distance underneath the soil floor. In lots of circumstances, just one plant is ate up, being partly or fully pulled underground and eaten.
- Huge holes in stems of older seedlings
Better larvae (L4-L6) are probably the most destructive and usually provide on the four-leaf level of maize seedlings. By means of this level, maize seedlings are much less vulnerable to pricey injury by way of larvae as a result of stems are too thick to bring to a halt fully.
On the other hand, a blank spherical gap is eaten into the plant’s stem. This sort of feeding injury isn’t normally observed, until intentionally wanted.
Manufacturers usually confuse cutworm injury with different maize pests similar to false wireworm (Somaticus spp.) and black maize beetle (Heteronychus arator).
The wear inflicted by way of black maize beetle and false wireworm is very similar to cutworms, however has a extra frayed look than in terms of cutworms.
The indicators seen above-ground, then again, correspond to that of a plant attacked by way of those pests and are visual as wilting of the central whorl leaf, adopted by way of wilting of all the plant.
The plant’s expansion level on the time of assault is essential with recognize to its skill to live to tell the tale cutworm harm. A plant reduce underneath the rising level is not going to get well. Seedlings injured above the expansion level might every so often regrow, however continuously don’t get well totally.
Host vegetation (weeds)
Aside from maize, different plants suffering from this pest come with groundnut (Arachis hypogaea), asparagus (Asparagus officinalis), sunflower (Helianthus annuus), lucerne (Medicago sativa), tobacco (Nicotiana tabacum), potatoes (Solanum tuberosum), sorghum (Sorghum bicolor) and wheat (Triticum aestivum).
As in terms of many different insect pests, weedy host vegetation play the most important function of their biology and behavior. Cutworm larvae usually feed on to be had weed species, the place they change into higher larval levels ahead of attacking seedlings of newly emerged plants. Overwintering is a commonplace phenomenon amongst cutworms.
Larvae slowly expand from eggs laid right through autumn and iciness will stay energetic underneath iciness weeds till they achieve the ultimate larval level.
It will probably due to this fact be stated that the presence of those weed species right through iciness months as much as planting just about promises the presence of huge larvae (probably the most destructive level) at planting time.
Because of this, weed control practices are usually advised and thought to be the important thing to a success cutworm keep an eye on within the duration previous to crop status quo.
As newly hatched cutworm larvae depend on weeds for a meals supply when maize seedlings don’t seem to be to be had, blank cultivation to take away weeds, 4 to 5 weeks previous to planting, is had to make certain that larvae starve to demise ahead of seedlings emerge.
On the other hand, since maximum farmers plant herbicide-tolerant maize, blank cultivation isn’t usually practised anymore, resulting in cutworm issues. This could also be the case in some conservation farming programs the place weeds are found in fields till as regards to the time that seedlings emerge.
It is going to due to this fact be vital to use herbicide to kill weeds 4 to 5 weeks previous to planting, with the downside {that a} follow-up software is also wanted after seedling emergence.
Whilst weeds is probably not provide on the time when manufacturers goal to plant, their presence 4 to 5 weeks previously will affect the abundance of cutworm populations.
It is strongly recommended that cultivated fields be stored naked of weeds and crop residues 35 days ahead of planting so as get rid of cutworms by the use of hunger.
Moreover, tillage carried out smartly ahead of planting brings larvae to the outside, leaving them uncovered and at risk of assaults from birds and frost.
By means of casting off weeds from fields, cutworm moths and larvae are disadvantaged in their most well-liked oviposition and feeding websites. The idea is thus that cutworm populations in conventionally tilled fields will have to be significantly less than fields working towards no-till.