Many people are looking for the silver lining from the recent cold spells. One potential upside is that hard freezes can often reduce insect pest populations the following spring.
Back-to-back cold snaps were experienced the first few weeks of January with temperatures reaching record lows of 14–17°F in southwest Louisiana, and approaching the single digits in the northeast rice producing regions of the state. These abnormal conditions are certainly capable of affecting the survival of insects over the winter.
While it is a general rule that insects don’t thrive in cold conditions, some pests handle freezes better than others. Many pests, which are native to the U.S., have overwintering strategies which allow them to avoid the coldest temperatures, while tropical invaders are more vulnerable. We will examine some of the winners and losers among rice pests and discuss how this may affect your management plans.
Rice Water Weevil
The most damaging insect pest of rice in Louisiana is the rice water weevil, Lissorhoptrus oryzophilus. Unfortunately, the cold temperatures in January will likely do little to reduce weevil populations. This pest is known to survive the winters in rice producing areas of northern Arkansas and southern Missouri where winter temperatures often dip below zero.
Weevils survive by huddling near the ground under leaf litter in wooded areas or by borrowing into clumps of bunch grass adjacent to rice fields. Once they are sheltered, weevils drastically slow their metabolism and survive through the winter on fat reserves built in the late summer and fall.
In late March and early April, adult weevils emerge from their winter hiding places and begin feeding on young rice plants. Because the offspring of the overwintering generation directly infest rice in the early spring, even minimal reductions in weevil survival would be of some benefit to rice farmers, although it won’t likely be easy to notice.
Persistent cold temperatures in February and March can push back the date of the weevils’ spring emergence which would be beneficial to rice producers. However, if weather conditions delay planting, that benefit will be largely nullified.
Rice Stink Bug
Similarly, the rice stink bug (Oebalus pugnax) is a native pest which can survive the winters of more northern rice producing regions by seeking shelter from the cold. Stink bugs have the added benefit of producing the first spring generation from feeding on weedy grasses, including vaseygrass and barnyardgrass. As a result, there are usually plenty of hungry stink bugs around just in time for rice to begin heading, regardless of winter temperatures.
The fall armyworm, Spodoptera frugiperda, is another native pest found throughout the U.S. rice-producing regions which isn’t greatly affected by winter freezes. This pest flies south for the winter. Populations survive the winter in southern Texas, southern Florida, and the Caribbean, then migrate north in the spring. Armyworms can sometimes survive mild winters in coastal Louisiana but that certainly isn’t the case for 2018. More typically, armyworms reach Louisiana in the greatest numbers in early May which won’t likely change as a result of the freezes.
Luckily, there are some pests of rice which aren’t quite as successful at surviving the cold. Stem borers including the sugarcane borer (Diatraea saccharalis) and the Mexican rice borer (Eoreuma loftini) are native to tropical regions and are considered introduced species in Louisiana. The Mexican rice borer is not known to occur north of Alexandria. The sugarcane borer is present in northeastern Louisiana but is not a major pest of rice there in most years. These stem borers spend the winter as larvae within the stems of weedy grasses and rice stubble. This provides some protection from cold temperatures, but survival is for several hours. Populations may have recovered by mid- to late-summer, but earlier planted rice should avoid severe stem borer infestations this year. Reduced stem borer pest pressure allows for more flexibility in selection of insecticidal seed treatments, and growers are encouraged to consider all options prior to planting.
South American Rice Miner
The South American rice miner (Hydrellia wirthi) is another invasive pest from the tropics which has been problematic in recent years. The pest is most troublesome in coastal parishes, and only low populations have been documented further north, indicating this species is not fond of the cold. Overwintering behavior of the South American rice miner is not well understood, but it is likely that the cold weather has reduced the potential for damaging infestations of this pest this spring.
Redbanded Stink Bug
Farmers who also grow soybeans will see the most benefit of cold temperatures. Populations of the redbanded stink bug (Piezodorus guildinii) are anticipated to be greatly reduced in 2018 as a result of the cold. Although 2018 won’t be the pest-free season some are hoping for, we should catch a few breaks this year. Benefits of reduced pest populations will be greatest to early-planted rice, and planting as early as conditions will allow is always encouraged.