The 2009 rice growing season in Arkansas was the wettest year on record for many reporting stations in the state, according to the National Weather Service. Oddly enough, July was the fourth wettest month with 11 or more inches of rain (3 or 4 inches is normal).
In the state’s Grand Prairie region, 19 of 31 days in July — a critical month for blast to develop on rice in the state — had rain.
Rice blast is caused by a fungus that needs free water to infect, and this was no impediment for the disease during last year’s wet summer. It also needs susceptible varieties and 50 percent of Arkansas’ rice acreage was planted to them in 2009. Furthermore, blast is favored by late planting and 20 percent of the Arkansas rice crop was planted after May 27.
To make matters worse, we planted susceptible varieties in fields that tended to favor blast; that is, fields unable to hold a consistent 4 inch, or deeper, flood during the growing season. Previous research has shown that deeper flooding minimizes blast, but some growers in 2009 turned off the pumps on these fields to reduce cost, increasing blast problems.
The result of all this was the most severe neck blast epidemic in Arkansas since the Newbonnet blast years of 1986 and 1987. An example of the level of damage was a field of Francis rice with 100 percent neck blast incidence resulting in a yield of only 62 bushels per acre despite having been sprayed twice with high rates of fungicide.
We inspected 52 very heavily damaged fields in 10 counties in east-central Arkansas and another 18 with moderately severe damage in six other counties in the northeast part of the state. Of the 52 severely damaged fields we inspected, 20 were CL 151 (rated very susceptible to blast); 17 were planted to Francis (very susceptible); 11 to Jupiter (susceptible); and four to Wells (susceptible). Of the 18 fields with moderately severe damage in the other 10 counties, seven were CL 151; five were Francis; four were Jupiter; and two were Wells. We also observed some damage in fields of Bengal and Cheniere. In every field with severe damage, there were problems with flood depth, at least with regard to managing blast disease.
It could have been worse but county Extension agents and consultants put the word out in early July about blast and many growers responded by pumping the flood up and spraying properly. For example, a Jupiter field managed with deeper flood and two well-timed fungicide applications yielded 201 bushels per acre while nearby fields with erratic flood depth and a single application yielded less than 120 bushels per acre.
Our modern rice fungicides are much better than what we had in the 1980s, but they have limits — especially when it is raining all the time. During “normal” summers, we “get by” with one fungicide application, or lower rates, or even improper timing because disease pressure is light.
However, July 2009 was not the type of month when partial fungicide measures were going to work well. Last summer, fields receiving the high rate of fungicide at boot split followed by a second application when heads were partially out yielded well. Untreated or single application fields under similar conditions were heavily damaged. It is critical to spray these fungicides preventively, because once the fungus is inside the neck or panicle, it is too late.
While blast management during the growing season is very important, it is also critical to start with the right variety. Clearfield 151 and Francis are great varieties where blast is not a threat, but terrible choices for sandy fields, furrow irrigation, or other systems that strongly favor this disease. While expensive, current hybrid rice varieties are the best choice for rice production systems that favor neck blast — like sandy, furrow irrigation, pivot rice, or intermittently flooded fields.
Current hybrids combine high yield potential with very good disease resistance, a recipe that is hard to beat. A good future choice for these systems would also be the recently released variety from the Arkansas breeding program, Templeton, that has good yield potential and very strong blast resistance.
While resistant varieties are an important fundamental in growing the best rice crop possible, it is also true that resistance to blast may not hold up forever in a given variety. Consistent planting of rice in the blast-favorable systems mentioned earlier will eventually mean races of the blast fungus able to attack hybrids, Templeton and other resistant varieties.
Since this is bound to happen in the long run, we continue to ask growers, consultants and county agents to help us stay in front of the blast fungus by notifying us of suspicious spots on the leaves or symptoms on the panicles of resistant varieties. We can inspect and confirm blast in these situations, and be forewarned of any changes in the fungus.
While 2009 was pretty tough as rice disease challenges go, conditions last year also showed us how stable our rice production system is and how good our technology and farmers are at managing problems and still producing a good crop overall. While blast put a dent in us, it could have been a lot worse. Here’s hoping for an easier rice season in 2010.