Rice growers toss away the calendar for this year

Issue Date: July 21, 2010

By Bob Johnson

Richvale rice farmer Ken Anderson stands in one of his rice fields in early July. The crop is several days behind normal because of the cool spring and numerous rain events that delayed planting.

For rice growers the difficulty in getting their crop planted this year was just the beginning of the challenges created by the unusual weather.

One of those challenges is determining the best time for mid-season herbicide and fertilizer applications, which depend largely on the weather in the weeks after planting. This is a crucial decision because applications that are too early can be inefficient, while applications that are too late can damage yields. The wide range of planting dates and unusually cold late spring weather have made it particularly difficult to locate the target date in 2010.

Close inspection of this rice plant shows that panicle initiation had not yet been reached, a stage of crop development that is an important indicator for determining herbicide or fertilizer applications.

Richvale rice farmer Ken Anderson was inspecting one of his fields after the Fourth of July weekend to decide if the time had come for a third and final herbicide application. Anderson used his pocketknife to carefully slice open a main tiller to see if the panicle initiation stage had been reached. It had not yet been reached.

“Once it reaches panicle initiation I don’t want to apply herbicides because it will harm the plant and really drop the yield,” Anderson said.

One of the consequences of the unusually cool period after he planted this field on May 20 is that the weeds germinated over a longer period of time than usual, which means Anderson will have to apply herbicide a third time to more of his field.

But the weather in the weeks following planting has also made it very hard this year to predict when the rice will reach the critical time of panicle initiation.

Anderson figures it normally takes 50 to 55 days after planting for his rice to reach that critical stage. But, 2010 is anything but normal. Not only did the clock start later in most rice fields, but the weather has also made it difficult to predict how long it will take the plants to reach panicle initiation because the early growth stages are largely determined by the weather.

“We were about a month late on planting, then after we planted it was cool for about a month. The days to harvest from heading is very predictable, but the first vegetative stage depends on the weather,” Anderson said.

Most rice growers face this challenge in timing herbicides this year.

“All herbicide applications need to be finished before panicle initiation, or else productivity may be compromised. Scheduling production operations that are growth stage sensitive by the calendar is unreliable in a year like this. Be sure to scout your fields to determine the actual stage of growth so that weed clean-up operations are conducted at the proper time,” said Cass Mutters, University of California Cooperative Extension farm advisor in Butte County.

Late planted rice that was not planted until June, like many of Anderson’s fields, may mature faster than usual because of the warm weather. But, rice that was planted earlier will mature more slowly.  It has been more than a decade since rice growers dealt with early season weather as cool as this year.

“Unless stressed by other environmental factors like moisture, the development rate from emergence to maturity for many plants depends upon the daily air temperature. Degree days are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature, which is 55 degrees for California rice. Using accumulated degree days for comparison, 2010 was the coolest start to a growing season since 1998 when we last experienced a strong El Niño effect in the spring,” Mutters said.

The unusual weather makes 2010 a good year for rice farmers to throw away the calendar in making decisions about timing herbicide and fertilizer applications.

“The calendar is just a guideline; you have to go out and look at your plants,” Anderson said.

The stage of plant growth is also crucial in timing fertilizer applications to get the biggest yield boost, and to avoid disease and lodging problems.

Anderson applied preplant nitrogen in May, and followed that with a sidedress application in the middle of June. If he applies additional fertilizer, he wants to target the application to the relatively short window between panicle initiation and panicle differentiation.

“The problem with going in too late is the plants are not going to use the nitrogen to increase yield. They are going to grow taller, which increases the chance of lodging. It also increases the chance of diseases,” said Luis Espino, UCCE farm advisor in Colusa County.

The consequences of making the final nitrogen application too early are less disastrous.

“If you’re too early you’re not going to have as much efficiency with the application. But some growers do go in early; it’s an option,” Espino said.

The crucial window between panicle initiation and panicle differentiation is only a week to 10 days, according to Espino.

“Most growers have the experience and can pull some plants, cut the main tiller with a sharp knife and see the green ring. Most of the early plantings are coming to panicle initiation very late. Growers who are used to scheduling their fertilizer applications need to go out in the field and look this year, because it’s going to be different,” Espino said.

Laboratory tissue analysis is a very reliable way to determine if the crop needs nitrogen. But this analysis has to be done quicker than usual to allow for an application during the narrow time frame between panicle initiation and panicle differentiation.

“Some labs can do it in two or three days,” Espino said.

Another approach is to invest in a chlorophyll meter, which will give accurate nitrogen readings in the field.

“Around this area chlorophyll meters are not used very much to decide if the plants need nitrogen,” Espino said. These hand-held devices are easy to use but the price tag – in the range of $500 to $600 – is a disincentive to widespread use.

The most common method of deciding if a final nitrogen application is needed is to come to a decision by looking at the plants.

“A lot of growers rely on their experience to look at the color of the crop,” Espino said.

Once the plants have reached panicle differentiation and all the herbicide and fertilizer applications are complete, then begins the nerve-racking waiting game.

The plants look good so far, but Anderson recalls that statewide yields have suffered in the past when rice is planted late because of the weather. And, the key question will be the weather at harvest.

“If we have a wet rainy fall it’s going to be difficult. Last year we started harvesting the first week in September and finished on Oct. 28. This year Oct. 12 is a guess on when we will start harvesting,” Anderson said.

(Bob Johnson is a reporter in Magalia. He may be contacted at bjohn11135@aol.com.)

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item. Top