Crop Scene Investigation - 26: What's ailing Art's alfalfa?
Wednesday, May 5, 2010
by BERNARD TOBIN
When it comes to scouting fields, it's tempting to do inspections through the windshield of your truck as you drive down the side road at 60 kmh. But farmers know it's important to put it in park and hit the dirt, especially in corn, soybean and wheat fields.
Joel Bagg, a forage specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, wishes forage fields, particularly alfalfa, were also on that list. Unfortunately, these fields too often get the drive-by treatment. Like other crops, it's also important to dig up forage roots to find out what's going on in fields that are not meeting expectations.
"The problem is that very few people ever do diagnostic work on forage," laments Bagg.
"People don't dig up alfalfa roots, rinse the soil off, take a knife and split them open.
We just do the windshield treatment."
To illustrate this point, Bagg shared a story from last summer when Art, a Durham Region dairy farmer, called him seeking advice on what he discovered while walking his alfalfa field.
"What he found in the field were big oval patches of short, stunted yellow plants," recalls Bagg. "He was disappointed because he just wasn't getting the production he was expecting from a third-year alfalfa field. He had a decent first cut, but the patches in his second-cut field had raised a red flag."
It was mid-July when Bagg arrived to inspect Art's alfalfa. "When I saw the field, I had a good idea what was causing the problem, but I had to eliminate a number of other possibilities. After I reviewed Art's soil tests and fertility program, I ruled them out. I also crossed off any herbicide-related cause – it was a third-year field that hadn't been sprayed since the establishment year. The field had survived the previous winter without any alfalfa heaving or winterkill.
"As I walked the field, I saw no evidence of any pest problems, such as potato leaf hoppers. Overall, the drainage was pretty good, but it was variable. Art explained that the field was not tiled and there were some heavier clays on parts of it.
"I then asked Art about the variety he had planted in the field. He said it was Rocket, a variety that had delivered him top performance over the years. He also had noted that it was treated with Apron seed treatment to help protect against pythium and phytophthora root rot. I took note of the variety and decided it was time to start digging some plants.
"As we looked at the stunted patches in Art's field, there appeared to be a definite separation between the affected patches and the normal plants – you could draw a distinct line between the two. I decided to dig up plants on either side of the line and do a direct comparison.
"The plants on the healthy side had big crowns, lots of stems per crown and were very vigorous. There were plenty of secondary roots, root hairs and a lot of nodulation. But the plants in the oval area were the complete opposite. There was no evidence of soil pests, but something was definitely happening underground.
"The yellow, stunted plants had small roots that lacked root hairs and secondary roots, and there was practically no nodulation. We would have to do some testing to confirm my diagnosis, but all the evidence pointed to one culprit."
Do you know what was ailing Art's alfalfa? Send your solution to Better Farming at: rirwin@betterfarming.com or by fax to: 613-678-5993.
Correct answers will be pooled and one winner will be drawn for a chance to win a Wireless Weather Station. The correct answer, along with the reasoning followed to reach it, will appear in the next issue of Better Farming. BF