Louisiana Rice: Pest Concerns for Late-Planted Crops
By Blake Wilson
LSU AgCenter Extension Rice Specialist
The recommended planting dates for Louisiana rice are March 10–April 15 for southwest regions and April 1–May 5 in the north. In an ideal world, all rice would be planted within those windows to maximize yield potential. In the real world, weather delays, equipment failures, labor shortages, or other factors can prevent timely planting.
Some farmers may opt to plant fields following crawfish production, pushing planting to well outside the optimum window. Yield is often reduced in late-planted rice by the stress from high summer temperatures. Insect pests and diseases are often worse in late-planted fields. Here are some considerations on how to approach insect management if you’re behind in getting the crop in.
Contrary to prior beliefs, recent evidence suggests rice water weevil infestations do not vary greatly among planting dates. High infestations can occur even in fields planted the first week of March, suggesting spring emergence of adult weevils may now be occurring earlier than in the past. Farmers should plan on controlling this damaging pest in all fields.
Conversely, extremely late-planted rice, such as fields planted for fall crawfish forage, tends to have reduced weevil damage as adults begin to move into over-wintering habitats. However, this is the exception, not the rule. Most insect populations continue building as summer approaches, increasing the likelihood that damaging infestations will occur.
Stem borers, particularly the Mexican rice borer, are much more problematic in late-planted rice in comparison to rice that is planted on time. Densities of blank panicles, or whiteheads, are three to four times greater in rice planted in late-April or May. Yield loss from borers alone in late-planted fields may reach 10–15%, with potential for greater losses under severe infestations.
Farmers should plant seeds treated with Dermacor X-100 or plan on scouting untreated rice for borer larvae from tillering to grain-fill. Scout for borers by removing leaf sheaths and looking for the presence of larvae. No thresholds have been developed for stem borers, but if you’re finding larvae, you should consider a foliar application of a pyrethroid.
Once whiteheads appear, it’s too late to achieve control. The damage is already done.
Armyworms, the other key Lepidopteran (caterpillar) pest, are also worse in late-planted rice. Defoliation of young rice can be severe in some cases, but rice can often grow through low to moderate levels of injury with minimal impacts to yield. Armyworm infestations tend to decline once the permanent flood is established, as larvae drown or become exposed to natural enemies.
As with stem borers, armyworm infestations can be controlled with Dermacor X-100 seed treatment or foliar pyrethroid applications. In both cases, pyrethroid applications should not be made to rice in a crawfish rotation.
Rice stink bugs are more mobile than Lepidoptera larvae and may become concentrated in fields that are in reproductive stages if no other headed rice is in the area. This may occur if a field is either the first to head in a given area, or the last. Regardless of planting date, rice should be sampled with a sweep-net from flowering to hard dough to guide treatment decisions.
Other, less-damaging pests are also worse in late-planted fields. The rice leaf miner and South American rice miner often injure young rice in late-planted fields. As with armyworms, rice tends to recover in most cases. Effective control strategies for these pests have not been identified, so most infestations should be left untreated.
Maintaining plant health through effective timing of fertilization, and weed and disease control, should allow rice to grow out of this injury without much impact on yield.
More sporadic pests, including aphids and chinch bugs, can also reach damaging levels in late-planted fields. If concerning infestations of these or other insects develop, contact an extension agent to help assess the situation before making treatment decisions.
Information on the full spectrum of rice insects is available on the LSU AgCenter website or in the Rice Varieties and Management Tips booklet.