Early Pest of Sorghum and Maize

As we all know planting time is single most important operation that we will do for the season, and unfortunately we get precious few opportunities to plant these day’s.

For these reasons it very important to make sure our emerging seedling are protected from seedling pests such as insects and mice.

By their very nature; attack from these types of pest is sporadic from season to season and field to field. Due to this it is very difficult to anticipate their occurrence and numbers, so regular inspection of emerging crops is essential.

Maize in particular is sensitive to plant spacing variation, growers in recent times have recognized the importance and yield benefits of even seed spacing and are going to considerable effort to ensure the best possible result. All this effort could be for naught if we ignore the risks of early pests. The effect of uneven plant spacing in maize is estimated to cost growers on average 400-500 kg/ha, this before insect and mice have had there share; for more information on the effects of seed spacing variation follow the  link to research from Purdue University http://www.agry.purdue.edu/ext/corn/pubs/agry9101.htm.

The most likely seedling pest we encounter are ground dwelling insects such as false wire worm and cut worm, above ground predators such as Northern army worm and mice, and sap sucker such as thrips and aphids.

The best defense against a lot of ground dwelling insects is an integrated attack which includes; good weed control, well controlled planting depth and evenness, sowing into good moisture, warm soil, quality seed treated with an insecticide. Even with best practice the desired result is not guaranteed, early planted crops usually come under the most pressure, false wire worm in particular are generally in abundance in the early part of the season, so planting without seed treatment is definitely not recommended.

Cutworms appear in a number of paddocks each year and unfortunately are not controlled by Cruiser® and Gaucho®, in furrow applications of chlorpyrophous may be successful if the cutworms are present, chlorpyrophous has very short residual control, so if eggs laid after the planting operation limited control can be expected.

Cutworm are very difficult to find in dark, moist clay soils as they are the same colour, in row crops planted with a twin disc they are often found at the base of the seedling in the seed trench. Damage to seedling is often the first sign of their presence, typically cutworm lop off the seedling at ground level at night and pull the green material into the ground for safe consumption. Fields close to pasture, weedy road sides or fields with heavy weed pressure are usually at risk, some species of cutworm like to lay their eggs under the leaves of weeds such as wild turnip and milk thistle. Chemical control typically revolves around surface sprays of chlorpyrophos applied late in the afternoon or at night. Control is usually adequate but under high pressure a second application is often needed and replanting with in furrow sprays has occurred. Please consult you consultant before application of any chemical.

Common Armyworm can cause severe damage to winter cereals and emerging summer crops, generally the moths lay in barley crops in September and October. The larvae prefer lush crops that provide good cover and protection. If larvae are not finished their development as the barley is haying of they can migrate to near by fields of summer crops. Bare patches on the edges of fields adjoining barley is a good indicator that armyworm may be present, low numbers in barley can cause high levels of damage in young summer crops. In dry years Armyworm damage can be mistaken for dry patches in the field.

Mice seem to be increasing in their importance as a pest of agricultural crops, damage caused by mice to agriculture is estimated at between 10-30 million. Recent surveys by the Qld NRW has identified some areas where mice numbers are on the increase and look like they will need controlling. Areas on the Eastern & Central Darling Downs are already incurring damage in winter crops and some baiting has already started. The western downs is at moderate risk and numbers around Mungindi are reported as high. Mice like to over winter in zero till sorghum paddocks and in table drains, as food supply diminishes in these areas they migrate to winter crops. If left uncontrolled they can cause high levels of damage in the winter crop and can move on to the summer crops. In my opinion they cause their worst damage in dry years were water and food are short, in these years they will attack developing heads in the stem or at the milky dough stage, causing much more damage if they just attack the hard grain for food.

Aphid numbers have been high in the barley and canary crops these are predominately oat aphid which can be found at the base of the plant where they are well protected, oat aphid do not usually infest sorghum and maize in Australia but have been a pest of maize in the US. Corn aphids are present in the upper leaves and the whorl of the barley and have started to migrate to early planted maize crops.

Control of aphids is not on either of the seed treatment label, however both Cruiser® and Gaucho® give good suppression for two to three weeks.  Corn aphid very rarely requires controlling these days as the number of disruptive sprays has been drastically reduced in the farming system. Aphid numbers can get very high in moisture stressed crops, it is very hard not to want to spray in these situations, however if left alone beneficial insect usually control these sticky pest. Spraying disruptive chemicals in the vegetative stage can cause bigger problems later with aphid and heliothis infesting the sorghum heads in particular.