SPRING FLEA BEETLE POPULATIONS IN CANOLA

        Fall populations of flea beetles in 2007 are generally indicative of the spring population levels in 2008.  If high populations are seen at harvest 2007, there will be high populations in spring 2008.  This past fall a total of 156 canola fields were surveyed in the swath (mature) stage for flea beetles in 24 counties in ND.  This number represents approximately one field surveyed per 6,000 acres of canola.  The survey was initiated on July 30 and continued through August 15, 2007.  Flea beetles were surveyed using 20 sweeps per field with a 15-inch sweep net in freshly swathed canola fields.  Flea beetles were found in 99% of the fields surveyed.  Peak population densities occurred in the north central and northeastern regions of North Dakota.  The average number of flea beetles per 4 sweeps was 24, with ranges between 0 and 94 (see map). These numbers are similar to the flea beetle populations that were found in swathed canola last year and represent low to moderate levels of flea beetles.

        Crucifer flea beetles overwinter as adults in leaf litter of shelterbelts or grassy areas and are rarely found in canola stubble. Beetles emerge in large numbers when temperatures warm up to 57^NF (14^NC) for several consecutive days and there is a rainfall event in early spring.  They feed on volunteer canola and weeds, such as wild mustard, and move to newly planted canola as it emerges.  Depending on the temperature and rainfall, it may take up to three weeks for the adults to leave their overwintering sites.  Warm, dry, and calm weather promotes flea beetle flight (flying up to several miles) and feeding throughout the field.  In contrast, cool, rainy, and windy conditions reduce flight activity, and flea beetles walk or hop which leads to concentrations in field margins.  When population levels are high, significant damage can occur within a 24-72 hour period.  The most susceptible growth stage to feeding injury is the first 14-21 days after emergence. 

        More than 90% of North Dakota canola fields receive  commercially applied seed treatments, like Helix XTra or Prosper FX.  These systemic seed treatments can provide protection against flea beetles for about 21-25 days after seedling emergence.  With the canola seed sitting in cool, dry soil conditions this year, crop emergence and growth is delayed.  Without actively growing plants, systemic seed treatments are not readily taken up into the plant and this may result in reduced insecticide toxicity, residue, and efficacy.  The take home message is to regularly scout seedling to 6-leaf canola for feeding injury - pitting (see photograph). 

        An action threshold of 25% injury would justify a foliar spray on top of the seed treatment.  Recent research indicates that the best insecticide strategy for management of flea beetle was the high rate of insecticide seed treatment plus a foliar insecticide applied at 21 days after planting, regardless of planting date.  The foliar spray on top of the seed treatment controlled later-emerging flea beetles as the seed treatment residual was diminishing and the crop became vulnerable to feeding injury.  The next few weeks will be critical for protecting canola against significant flea beetle damage!

Note:  Funding for the canola survey was provided by the Northern Canola Growers Association and CSREES Canola Research fund.

 

 Wheat streak mosaic

        Wheat streak mosaic virus is carried from plant to plant by wheat curl mites.  Wheat curl mites are very tiny (1/100 in long).  Their populations generally increase rapidly under extended warm dry weather, and with high mite numbers the chance of infection of susceptible crops becomes higher.  The mite transmits the virus during feeding and the virus infection causes yellow streaking of leaves, stunting of the plant, and reduced yields.  The mite needs a green bridge for survival; it frequently overwinters on winter wheat or perennial grassy weeds, and then moves from these plants to adjacent spring grains in the spring or early summer.

        Mites move more frequently during heat and drought stress, seeking green, healthy plant tissue. They move to the outer edge of leaves where they are positioned for easy movement in the wind to adjacent healthy plants.  The virus disease severity is greater under drought stress because the plant has fewer nutritional and water resources to compensate for virus infection. 

 

Wheat streak mosaic management: Wheat streak mosaic is managed by two cultural practices: elimination of volunteer wheat plants and grassy weeds with herbicides or tillage at least two weeks prior to planting a new grass crop, and use of appropriate planting dates.  Each practice helps to break the green bridge needed for mite survival.

        Elimination of volunteers and grassy weeds: At this time of year, control should be directed at any infected fields prior to replanting.  Roundup or other glyphosate-containing compounds may be used to destroy infected hosts.  This should be done two weeks prior to planting a new, susceptible grass crop into that field or adjacent field, because the herbicides act slowly to kill plants, and mites on these plants will move out of the infected volunteers for up to 10 days after herbicide treatment. 

        Planting dates: Replanting a spring grain into a field with previous infection at this time would be risky.  Wheat curl mites continue to develop and increase populations during warmer months.  A late planted spring wheat crop could be infected at emergence and be severely damaged.

Additional information about wheat streak mosaic disease may be found in NDSU Extension Circular PP-646 “Wheat Streak Mosaic” http://www.ag.ndsu.edu/pubs/plantsci/smgrains/pp646.pdf

 

 PREPAY FOR 2009 FERTILIZER?

        I have received several questions regarding the wisdom of prepayment of fertilizers for the 2009 crop. This is odd because the 2008 crop is not yet entirely seeded, with fertilizer decisions still remaining for this growing season. Although I am certainly not a seer by trade, and don’t have a 900- number that one might call for this information, I will offer my insight into why these offers might be happening and what I would do if I were confronted with this issue. Having spent eighteen formative years in the retail fertilizer business, I have at least some background to help form these thoughts.

        There are several reasons for offering a prepayment for fertilizer and other ag-goods. The first is to lock in business for the next season. The second is to help with cash flow. The third might be to bail out of higher priced goods knowing that next seasons costs will either remain the same or go down.

        The first reason might explain discounts to products and services offered before the first of the year. Prepayment for spring is common during December and early January for winter/spring delivered goods and services. However, I do not think this is the reason for wanting a grower to lock in product now.

        The second reason is a major consideration for retail/wholesale businesses right now. Two years ago, the entire fertilizer purchase for spring by a company might be $20 million. This year, with rising costs, the credit required might be $60 million. There is a credit problem in the entire country according to news sources that is far larger than just agriculture. In a normal credit environment tripling a credit line would be difficult. In a tight credit market, increasing credit lines is even harder. Therefore there is incentive to encourage prepay to help cash-flow. This is particularly important since decisions for retailer “fall-fill” for fall applications need to be made really soon to have product on-hand in September-November.

        The third reason may or may not be happening. It is difficult to know. However, in my experience, if product were really tight businesses seldom offer prepay. Why take less money now if you are guaranteed more later? Doesn’t make much sense. Prepayment is usually only offered if there is adequate product on hand. Also, if I were stuck with several hundred tons of product that tripled in price in the last 6 months, but people lowered the product they bought due to the price and I was stuck with it, I would want to get rid of it before the price dropped to half of what it is right now. I heard a report that the prepayment for MAP was $1,200/ton (today’s price) but that it was probably going to $1,900 next year according to the prepay source. I will boldly take the opinion that the chances of MAP going to $1,900 are incredibly slim and if it did, no one would care because no one could afford to buy it. Our data show that on low testing P soils, a yield increase for most crops would be about 25%. Given a yield potential for wheat on fertile soils in central ND of 40 bu/acre, that means that without P, yield might be 32 bu/a. Our current recommendation encourages application of 40 lb P₂O₅ (about 80 lb/a MAP) under those conditions. 8 bu/a wheat at $7/bu is a $56/acre potential return from P. The MAP required to make that happen would cost $76/acre at $1,900/ton. Even at $1,200/ton, the return would be under $10/acre. Given the risk at putting in the crop, I would suggest to producers that with MAP at $1,200, they should only put on half of a normal rate. The response curve of crops to P is curvilinear, meaning that the greatest increases are due to the first ½ of the application rate. So you lose a couple bushels by not putting on the full amount, but you might gain $10/acre and don’t have to borrow as much or risk as much. Growers cannot and will not apply as much fertilizer at current or higher prices. So I believe that the chance of prices going lower are good.

        My recommendation? Prepayment in the fall for spring needs is good. Prepayment in the spring for next springs needs is probably not good.