• By Jeff Gore, Don Cook, Whitney Crow and Angus Catchot •
A lot of rice has been planted in the state over the last couple of weeks, and most of it had an insecticide seed treatment as we recommend. The most common insecticide seed treatments in rice are one of the neonicotinoids Cruiser or NipSit.
All of our research over the past 10 years or so has shown that those seed treatments provide a net economic benefit about 80% of the time with an average 8.3 bushel per acre yield increase over fungicide only treated rice.
Our research has also shown that the neonicotinoids don’t provide absolute control of rice water weevil, and we saw benefits of foliar sprays with pyrethroids to improve rice water weevil control in a lot of situations. The benefits of additional control over that achieved with a neonicotinoid seed treatment are more common when adverse weather conditions slow rice emergence and early season growth.
The neonicotinoid seed treatments are very water soluble, which means they don’t last very long. The clock starts ticking on their longevity when the seed goes in the ground, not when the plants emerge. We are asking a lot out of seed treatments in rice because we need them to still be effective when we put the flood on the field. This can often be several weeks after planting. The treatments still work, but they may not work as well as we would like in some situations.
As I’m writing this today (April 21,), the low temperature this morning was around 40 degrees Fahrenheit and the lows are expected to remain in the 40s for the next couple of days. The conditions are not ideal for rice emergence and development and that is likely going to affect the performance of neonicotinoid seed treatments. The main point is that seedling growth has been slow over the last week and that will likely affect the performance of seed treatments.
The other seed treatments currently available in rice include the diamides Dermacor and Fortenza. The real strength of these insecticides is that they are much less water soluble than the neonicotinoids and last a lot longer than the neonicotinoids. We have seen benefits of using either of these insecticides even when added to neonicotinoid seed treatments.
The slides below are results from studies we conducted across the Delta in 2019. The first graph shows yields from small plot trials in flooded rice conducted at three locations across the Delta. As you can see, the CruiserMaxx rice averaged 11 bushels higher than the fungicide only, and the CruiserMaxx + Fortenza rice averaged 12 bushels higher than the CruiserMaxx only.
The bottom graph shows yields from large strip trials at five locations across the Delta in Row Rice. In that situation, there was still a 7 bushel yield benefit for using Fortenza was used. Similar results would be expected with Dermacor.
The diamides are considerably more expensive than the neonicotinoids, so it is often difficult to decide whether or not to use them on top of an already expensive seed treatment package. This is especially true on a conventional variety, but they can be more affordable on a hybrid with lower seeding rates.
Most of the time, the diamide seed treatments like Dermacor and Fortenza will provide an additional level of yield protection that will pay for the treatment. The other option is to wait and see what happens and potentially have to make a pyrethroid application for rice water weevil control later in the season.
By Drs. Jeff Gore is a research and Extension entomologist, Don Cook is a research entomologist, Whitney Crow is an Extension entomologist and Angus Catchot is an Extension entomologist. All are with Mississippi State University.