While scouting for blast, a PCA noticed some yellow leaf tips. Close inspection revealed aphids. He got a little worried since he's never seen aphids on rice during his long career. They turned out to be yellow sugarcane aphid. These aphids are common in small grains like wheat and barley, and in corn, so it is not surprising that they can be found feeding on rice. Actually, they are considered a pest in southern rice, where they feed on rice during the seedling stage. 

Photo by Bart Drees, Texas A&M University

We went to the field to see how prevalent they were. There were some yellow leaves above the canopy level. These were mostly from bakanae infected plants. There were some yellow leaves here and there at the canopy level, on these we found aphids. 

Yellow sugarcane aphid injects a toxin into rice plants during feeding that causes the foliage to become reddish.

In California, aphids are not considered a pest of rice. Most likely, they are present in some rice fields some years at very low levels, and mostly go unnoticed. The infestation in this field was very low, and probably the aphids will disappear in a few days. Nothing to worry about - just something to be aware of.

While looking for the aphids, we noticed some feeding scars that, at first, looked like rice water weevil scars. After looking closely, we realized these were caused by something else. After some search, we found quite a few beetles feeding on the rice next to the road.

I haven't identified the beetles yet, but they look and jump like flea beetles. The field is next to some unmanaged vegetation, and most likely their food source is drying off, so they are looking for some green material. I think this is just an "incidental" infestation. Again, nothing to worry about - just something to be aware of.

Research conducted by Albert Fischer and James Eckert, Department of Plant Sciences, UC Davis, has confirmed that some populations of smallflower umbrellasedge from rice fields in the Sacramento Valley have become resistant to propanil. Following is a summary of their findings.

Smallflower umbrellasedge seed from eight fields where resistance was suspected was collected and germinated in the greenhouse. Plants were grown in pots and, at the 2-3 or 4-5 leaf stage they were sprayed with SuperWham, UltraStam or RiceShot at half field rate, recommended field rate, and twice field rate. Both spray timings produced similar results, but the earlier application produced the most striking results.

Table 1 shows the percent control of smallflower umbrellasedge when sprayed with 3 formulations of propanil. For simplicity, I'm showing only the results of the application with 6 lbs a.i./a. Percent control of smallflower umbrellasedge from fields 4, 6 and 8 was very poor, between 6 and 45%. Control of smallflower umbrellasedge from field 3 was mediocre, between 62 and 74%. And control of smallflower umbrellasedge from fields 1, 2, 5 and 7 was very good, between 68 and 100%.

 

Table 1. Percent control of smallflower umbrellasedge with 3 formulations of propanil applied at 6 lbs a.i./a.

Smallflower umbrellasedge from fields 1, 2, 5 and 7 can be considered susceptible to the formulations of propanil applied. They were tested because control failure had been observed in the field. Results from the greenhouse tests suggest that something went wrong with the field application. For example, the application could have been made too late, coverage may have not been appropriate, there could have been incompatibility in the tank mix, wrong application rates might have been used, etc. Populations from fields 3, 4, 6 and 8 can be considered resistant. This prompts the question, what are the options to control these populations?

To answer this question, another set of greenhouse tests were conducted to evaluate herbicide options for propanil-resistant smallflower umbrellasedge. Results (Table 2) show that propanil-resistant smallflower umbrellasedge was also resistant to Londax, resistant or partially resistant to Granite SC and Sandea, and susceptible to Shark H2O when applied as a foliar.

 

Table 2. Percent control of smallflower umbrellasedge with alternative herbicides.

 

Results suggest that in fields with propanil-resistant smallflower umbrellasedge, Shark H2O could be used to achieve control. In fields where resistance is not a problem yet, the best approach is to alternate modes of action whenever possible. If you suspect you have propanil-resistant smallflower umbrellasedge, collect seeds at the end of the season and take them to the Weed Science project at the Rice Experiment Station in Biggs for screening.

Armyworms are common in rice fields from mid-July to August. Two species can infest rice, the armyworm and the western yellowstriped armyworm. These insects build up their populations in alfalfa, other grains and grasses, and invade rice late in the season. The adults are moths that lay their eggs either on rice leaves or on broadleaf weeds within rice fields. After the eggs hatch, the small larvae begin feeding on rice foliage and/or panicles. Young larvae are hard to see, they can be less than a quarter of an inch long and their color mimics older rice foliage. Larvae go through a series of molts, growing to 1.5 to 2 inches. When they are ready to pupate, they drop to the ground in search for a good pupation site in the soil. In rice, they usually drown. I have seen armyworms pupate in the leaf sheath of older leafs at the base of plants at the water level, but this is uncommon.

Foliage feeding does not affect yield unless the armyworms consume 25% or more of the crop's foliage. It's not uncommon to walk a rice field and find areas where feeding is noticeable. In those areas, open the canopy and look near the water level. You might find armyworms resting there during the day. At night or when it's cooler, they will climb up the plant and continue their feeding. Take notice of the size of armyworms you see – if most of them are small, they will continue their feeding and a treatment might be needed. If you can't find any armyworms, they probably have already completed their cycle and there is no need to do a treatment.

Armyworm damage can be more problematic during heading. Typical panicle injury consists of blank panicle branches, although sometimes the whole panicle can be blank. What happens is that the armyworm bites the rachis of the branch and the grains in that branch don't fill. Sometimes, armyworm injury can be confused with cold temperature blanking. However, if you look closely at the blank panicle or branches, you will see a chewing mark where the blank area begins. Inspect your fields as the panicles come out of the boot – I believe this is when most of the armyworm damage occurs. If after inspecting your field you find that 10% or more panicles are affected, and you can still find armyworms, a treatment might be needed.

For the most part, armyworms are not a major problem in California rice. Some growers experienced severe infestations last year; heavy infestations seem to be cyclical and return every few years. Luckily, armyworms have several natural enemies in rice fields that are very good at keeping their populations down. Birds are important armyworm predators and can function as a warning system for their presence in the field.

 

Up until today, I hadn't seen any blast in the area, but I got a couple of calls today of growers having to put a fungicide because of blast. We'll see if this year blast will be as bad as the past two years. 

Scout your fields and keep in mind that M-205 and M-104 are the most susceptible varieties we have. Draining and high nitrogen rates can increase the severity of blast. Below I'm re-posting some pictures and comments about blast.

 

Leaf blast symptoms of the disease begin as small grayish, whitish or bluish spots that enlarge to form diamond shaped lesions.

Lesions can coalesce and cover most of the leaf blades, causing "holes" of dead plants. This holes are usually observed at the edge of the field, in areas where nitrogen was overapplied because of overlap during aqua application. Excess nitrogen make plants more susceptible to infection.



Neck and panicle blast are of economic importance. Infection of the panicles directly reduce yield by causing empty heads that produce little or no grain.



Environmental conditions that favor the disease are extended periods of free moisture on the surface of the plant, night time temperatures between 63-73 F, no wind and high relative humidity.

When treating for blast, time your applications so that the young panicles are protected as they emerge from the boot. The fungicide azoxystrobin inhibits spore germination, and therefore is more effective when applied as a protectant. When using a fungicide, follow label directions and rates.