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Insect pest alerts

This month’s topic is late-season management, which is just as important as early and mid-season management. You are getting closer to the finish line, but don’t let up – keep scouting your rice for nutrient problems (remember, do not allow your rice to run out of nitrogen at this critical time), diseases, insects and weeds. Any stress, biological or otherwise, can hurt your yields and possibly delay maturity. Also, if you are planning to ratoon crop, be aware that a healthy, vigorous main crop transfers over to your ratoon crop.

Since I am an entomologist, I will discuss some late-season insect pests you may encounter. The rice stink bug invades rice fields when the crop begins to head. I do not recommend treating before heading, although some farmers add a pyrethroid to their fungicide and apply at late boot. Very few stink bugs are in your rice field prior to heading (they feed on developing grain or grass seeds), and pyrethroids do not possess a long residual activity, so applications before heading probably are not cost-effective.

Treatment thresholds for rice stink bug have recently been revised. Basically, the new thresholds are about three times higher than the old thresholds, which means, in general, you should not have to spray as much as in the past. We are in the process of trying to obtain a Section 18 Emergency Exemption for Tenchu 20SG (active ingredient = dinotefuran) for Texas rice farmers. Our data suggest excellent residual activity up to about 10 days, which is very good. Observations from the field in 2008 confirm this long residual activity.

EPA will make a decision in the very near future because rice planted early in March will be heading the first of June. This is when the season for rice stink bug begins. Let’s hope this excellent tool will be available to Texas rice farmers this season. I will keep you posted of any new developments.

Another serious late-season pest is the stalk borer complex made up of the Mexican rice borer, sugarcane borer and rice stalk borer. Texas populations are primarily Mexican rice borer and sugarcane borer.

Research has shown stalk borer moths do not begin laying eggs until rice is close to panicle initiation. We do not know why they do not infest rice earlier. In historically heavily infested areas like Jackson County, we recommend two applications of a pyrethroid – the first application at one- to two-inch panicle and the second at late boot/early heading.

Also, as you know, Dermacor X-100 (active ingredient = rynaxypyr) was granted a Section 18 Emergency Exemption in Texas this year. Our results show Dermacor X-100 as a seed treatment controls stalk borers. We are conducting more experiments this year evaluating the effects of Dermacor X-100 on ratoon crop pests.

Other late-season pests are grasshoppers. Some of our farmers spray for these critters, but I seldom see a field needing grasshopper control. In fact, one common long-horn grasshopper (actually a katydid) feeds on other pest insects! Usually, grasshopper populations are highest near field margins, so walk into the field at least 60 feet to properly sample these insects. Grasshoppers have chewing mouthparts and can attack developing panicles and foliage. Treatment thresholds are high – do not consider spraying unless defoliation approaches 20 percent, and grasshoppers are present.

Finally, I occasionally observe high populations of leafhoppers (primarily blackfaced leafhopper) on maturing rice. These insects excrete a sugary substance called honeydew upon which sooty mold fungi feed. This produces a layer of black fungi on leaf surfaces. Direct feeding by leafhoppers can also cause “hopperburn.” Damaged foliage takes on a bronze-gold color.

Signs also include cast skins of the adults and nymphs, which you can easily see on the surface of the foliage. Populations must be very high to produce hopperburn. Leafhoppers are easily controlled with a variety of insecticides. For more information on any of these pests, please contact me at (409) 658-7394.

However, you will not see any of these pests unless you get out of your truck and into your field. Set up a regular time for walking your fields – leave your cell phone, iPod and other electronic gadgetry in your truck; strap on your boots; get out your hand lens and pen knife; take an obsolete note pad and pencil; carry a bottle of water (tap is good) or other preferred beverage and step off into your own wildlife sanctuary – your rice field!


Rice stink bugs


As producers move through the season, it is important to closely monitor the rice crop. Even though rice may be heading, scouting for rice stink bugs is still necessary. Rice stink bugs can often be overlooked and not controlled. Rice stink bugs will reduce yield early in the heading stages and will lower the milling quality if present in the later stages of heading.

The last couple of seasons, rice stink bugs have been relatively light. Considerations of an insecticide application still need to be made if rice stink bugs are at or above threshold levels.

Once the rice begins to head, scouting for stink bugs needs to begin. I would begin scouting with a sweep net around the edges of the field and move towards the middle of the field. Sometimes stink bugs can be found just around the edges of the field. If this is the case, I would recommend applying an insecticide around the borders. This will control the present population and keep them from building up to be a bigger problem. Also, fields that have escaped grass present are more prone to have rice stink bugs. Therefore, keep a watchful eye on those fields.

Stink bugs are more detrimental towards yield during the first two weeks of heading because they are affecting kernel development. The current economic threshold for Mississippi is five stink bugs per 10 sweeps during this time. If stink bugs are a problem then, I lean towards the use of a pyrethroid insecticide. This will give you a couple of days of residual activity for longer protection.

As we move into the third and fourth week of heading, our economic threshold increases to 10 stink bugs per 10 sweeps. During this time, stink bugs are feeding more on mature kernels; therefore, a reduction in grain quality (pecky rice) becomes more of an issue.

The following pyrethroid insecticides are currently labeled and recommended for rice stink bug control: Karate Z (1 gallon/50 to 80 acres), Mustang Max (1 gallon/32 to 48 acres) and Prolex (1 gallon/62 to 100 acres). The old standby of methyl parathion 1/2 pound/acre or 1 gallon/8 acres can also be used.

One last reminder about stink bugs is to scout early in the morning or late in the evening. As temperatures rise through the day, stink bugs will generally move down into the canopy. If you are scouting during the hottest part of the day, take that into account when determining when to spray or not to spray.


Applying fungicides

In this article I want to clear up a few points about fungicide use and about drain timing. I’m thinking about the end of last year when Hurricanes Gustav and Ike caused so many problems with harvest.

The first issue to clear up is the use of fungicides, in particular, their timing. It is almost a standard practice now for many farmers to apply fungicide as insurance without scouting to determine need or proper timing. Most of the time that is probably OK, but there are cases when it is not.

Our verification field in Concordia Parish in 2008 was planted to CL 161, a variety known for its susceptibility to sheath blight. The plant population was high, and we recommended a fairly high nitrogen rate – two factors known to contribute to disease development. We picked up sheath blight when the rice plants were showing 3/8- to 1/2-inch internode elongation, much earlier than we wanted to apply a fungicide. Several years ago, Dr. Groth told me the earliest fungicide application for sheath blight control should not be until panicle differentiation (PD) + five to 10 days. We have adhered to that in the verification program since then.

We continued to watch the disease progress over the next three weeks. When the plants reached the 1/2-inch panicle stage, we recommended 21 ounces of Quilt + six ounces of Quadris. This application provided the equivalent of 12 ounces of Quadris and six ounces of propiconazole.

I know that seems like a lot of fungicide. Here is the logic: 1) we had a very susceptible variety; 2) we had heavy disease pressure; 3) we had to apply the fungicide relatively early; and 4) the field was showing signs of excellent yield potential. It turned out to be the single most critical decision we made that year.

Tropical storm Fay dropped 11 inches of rain on the field after it was drained for harvest preventing timely harvest. Then Hurricanes Ike and Gustav really flattened the field. The heavy dose of fungicide preserved much of the grain integrity.

Before the hurricanes, a small area of the field had been harvested. Yield measured there was 11,448 pounds per acre (71 barrels or 254 bushels) at 12 percent moisture. After the hurricanes, yield was 7,178 pounds per acre (44 barrels or 160 bushels). I am certain without the fungicide that losses would have been even greater.

In the verification program, we do not use a single fungicide rate or timing on all fields. Each field is considered as a separate crop. The more susceptible a variety, the higher the rate of fungicide needed. The heavier the disease pressure, the higher the rate of fungicide. The earlier the fungicide application timing, the higher the rate of fungicide required. The greater the yield potential, the higher the fungicide rate (especially if a ratoon or second crop is planned).

This philosophy has worked for us for several years. In another field, yield potential did not appear to be good and disease pressure was light, so we used a low rate of fungicide applied as late as we could. Like the field in Concordia Parish, it was a good decision because the hurricanes flattened it, too.

Drain timing has been a somewhat contentious issue for the past several years. I have and remain an advocate of keeping a field flooded for as long as possible. The weather last year caused me to question my judgment especially after tropical storm Fay. Hurricanes are such major events that I do not try to plan around them. Had we anticipated the rain of the tropical storm, we might have been able to harvest more of the field before the hurricanes. It is always easier to look backward than forward to know what you should have done that what you should do.

One thing I do not think I have made clear in previous discussions of draining is that it is not always necessary to actually drain the field. In some years, we simply stop pumping and let the plants use up the remaining water. Levees still have to be opened as if the field is being drained just in case rain comes along. But, in many cases there is little standing water in the field. On heavy clay soils, it takes about three weeks between drain and harvest, while on the prairie soils of the southwest area, it is about two weeks.

If we can perfect the use of the high-moisture meter we have been experimenting with for the last two years, we may have a more precise method of determining drain time based on grain moisture than our present method based on grain color in the panicle. No-till fields are usually firmer, which might allow water to be held longer in very hot dry years because they will support the harvest equipment better than prepared seedbeds.

I know I am going to pay closer attention this year to long-range predictions regarding hurricanes and tropical depressions when thinking about draining.


Drain timing options

Traditionally, choosing the right time to drain a rice field in preparation for harvest in California is an exercise in uncertainty wrought with anxiety. The decision is, of course, based on grower experience, but the criteria used are usually subjective.

There are occasions when a grower will drain a field only to re-flood it a few days later based on a reevaluation of the crop and weather conditions. With older California varieties, such as M202, this concern is warranted because of their sensitivity to late-season moisture stress. If M202 is drained just a few days too early, the yield and milling quality can be markedly reduced.

In contrast, based on work conducted at the Rice Experiment Station, fields planted in the newer and most widely grown medium grain varieties M205 and M206 can be drained 20 days after 50 percent heading (DAH) with no loss in yield or quality in heavy soils. This is about a week sooner than can be done with traditional medium grain varieties.

Growers in shallow or lighter textured soils may need to delay draining by a few days. Average 50 percent heading for M205 is 95 days after planting and 90 days after planting for M206. Fewer days are needed to reach 50 percent heading for both varieties if they are planted late when the temperatures are consistently high.

Draining the field for harvest based on the plant growth stage is a management tool that has not been available to California rice growers. Draining based on the stage of plant development allows growers to predict drain date several weeks ahead of time and better plan their harvest operations.

Understandably, counting the number of emerged heads in many fields may be impractical given that preparation for harvest season is a very demanding time of the year. In practice, a good approximation of 50 percent is possible based on general field observation, the “drive-by” technique. About four to five days following the appearance of the first heads in a field, there will be flush of emerged heads, and this is approximately the time of 50 percent heading. Cut the water off 20 days after that date.

Under experimental conditions, we pull the boards and drain the fields. Alternatively, the irrigation water could be halted and the water held in the field and allowed to seep into the soil. It this case, the water delivery would be stopped several days sooner than 20 DAH. This non-traditional approach to field draining will certainly require some fine-tuning for individual fields. Growers should try the technique on a small acreage until they become comfortable with the approach.

California is in the third year of a drought. While we in the northern part of the state were fortunate to have ample water for rice production in 2009, many growers in the San Joaquin Valley were forced to deal with substantial cuts in water delivery and fallow thousands of acres of farmland. Carefully chosen drain times may afford the flexibility in water management that results in measurable reductions in water use and pumping costs for the industry. In times of water scarcity, improved drain time management could not only improve grower returns but also reinforce the message that the rice industry is a good steward of the state’s water and energy resources.

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