If you are in the relatively small areas where the alfalfa weevil is a problem, you are aware of it and the only control is insecticide application.
The only other insect considered to be serious is the leafhopper. Leafhoppers over-winter within 100 miles of the Gulf of Mexico and are carried up on spring winds arriving in late May and June. They need time to built up to economic damaging populations, which is why they are more often a problem in seedling stands. Cereal grain (a grass) in seedling stands offers some leafhopper control as well as important erosion control. Seedling year stands often can use insecticide treatment. Leafhopper resistant varieties offer some control, but since the glandular hairs are not fully expressed seedling year, they too, often can use treatment. After the seedling year the leafhopper is less of a problem, especially if harvest interval is 35 days or less. Most seed companies are placing these varieties in special trials with only leafhopper varieties and are not sprayed with an insecticide. The comparisons are with older check varieties or with other lower yielding leafhopper varieties. Interestingly, I looked up yields of leafhopper resistant varieties at 'compare varieties' and found yield declined considerably after the second year compared to the test mean, while Vernal and leafhopper susceptible varieties did not. Is this because leafhopper resistant varieties have an advantage without insecticide treatment seedling year, and this advantage is being carried over into the first full year or is this due to some other reason.
Solution: In most cases, seed a cereal when establishing alfalfa for erosion, leafhopper and weed control. Utilize this forage for less demanding animals or spray out with a non-crop injuring grass herbicide. With or without companion cereal grasses, scout for hoppers 40 days after seeding. Use leafhopper resistant varieties only if you are in an area of severe leafhoppers and will not use insecticides or IPM (integrated pest management).
This excellent articleat the University of Wisconsin will give you understanding of this insect which will aid you in management decisions.
This was from a recent conversation with a crop consultant who was making a blanket statement recommending the leafhopper resistant varieties.
The consultant
The Iowa tables certainly support my contention that in picking the best LHR variety there's little at risk and much to gain.
My response
With the exception of Pioneer, all LHR varieties are coming from the Forage Genetics breeding program. There has never been a hot or high yielding alfalfa variety. That should be quite obvious when you look at how little progress has been made over Vernal, a variety over 50 years old. There have been many poorer yielding varieties, usually the first one coming out with some new trait and likely due to inbreeding. One reason we don't get an occasional hot alfalfa variety is we use many parents to avoid inbreeding and many parents approach average. The reason this one variety is looking good is chance or experimental error in the few tests you are looking at. If you want to make a comparison between two varieties, the LSD is what you use. If you want to compare all varieties, or pick the best variety, then the Duncan Multiple Range test that would have a wider range, is what you use to give you an idea of the value or faith you can put in your selection. The variety you are choosing could very well be a little better than other LHR varieties, but I can assure you, not much. About 1 year in 3 is what we see here (southern MN), except for seedling year that is at least every other year. The seedling year needs to be sprayed anyway and 1 year in 3 means about 1 cutting in 9 might need treatment. The data I have seen, that I have to base my reasoning on, is the LHR varieties are at least 5% below the best conventional varieties that isn't going to make up 1 cutting in 9.
The consultant
Interesting about the glandular hairs not being the main source of resistance. That's different than Pioneer was once saying. I also find it interesting that the author in the paper, right above the part you underlined about spraying LHR varieties in the seeding year, he makes the statement that "from then on yield of the unsprayed resistant line was identical to that of the unsprayed susceptible variety"
My response
The people selling LHR varieties have to recognize that seedling year LHR varieties are not completely resistant because they turn yellow. Resistance is good after the seedling year, but why would you accept a salesman word that yield is identical. He says identical to the unsprayed susceptible variety, not the best unsprayed susceptible variety.
The consultant
I mentioned your comments to a custom applicator/seed dealer. He said that is completely wrong; he's seen fields severely affected, and routinely recommends LHR alfalfa to his growers. He says the farmers who have used LHR varieties are very pleased and continue to use them. Remember, we're talking about trading a potential of a tenth of a ton or so of yield potential (difference between the best LHR varieties and good non-R varieties) for not having to worry about what is in this region a serious problem one year in about three. We probably won't ever agree with this, and I acknowledge that at least for the time being there is a small yield difference between the older LHR varieties in university tests and the best of the best, (other new ones) but even knowing this I'll stick to my guns. Thanks for the information.
My response
I have to go by data available. Virtually the only data is the Pioneer 54H91 variety. For the 2nd year (50 tests), through 4th (30 tests) harvest year, it yields 9/10 of a ton less or 3/10 ton per year less that the test means. Certainly, I could find a variety another 2/10 to 3/10 ton better than the test mean. I think you pulled the 1/10-ton out of a hat. I'm basing the half-ton on data I have, not data I hope to see. If your producing 4 ton and it takes 2 ton to cover production costs, a half-ton is a big deal. The LHR varieties have been lower yielding for 4 or 5 generation, what evidence do you have that they are now good yielding.
I just realized I could compare Pioneers LHR variety, 54h91, with a good standard yielding variety. I have noticed Pioneer 54v46 does very well in trials. I found there were 34, 27, and 19 comparison for the 2nd, 3rd, and 4th year and that 54v46 yielded exactly 0.49 tons more per acre per year. I cannot make that comparison with FG varieties since they are in so few standard tests, but I don't have reason to believe they would be much different.
I'm not aware that the seed companies even give blanket recommendation for LHR varieties. I think LHR varieties are a good thing when used properly, which I believe is an area at latitude central Iowa into Missouri and east. I think even in these areas it should be pointed out LHR varieties need treatment seedling year and have considerably less yield potential than treated standard varieties.
There were some IPM studies in IA, where they were leaving uncut strips, either as refuge for LH enemies (including a fungus disease) or as LH traps that could then be treated. If leafhoppers leave the field and then reenter, then it would seem leaving the back swath as a trap, and then treatment, which would mean a small tractor with a small inexpensive 3-point hitch sprayer and a few gallons of insecticide would do a good job. We don't seem to get much of this kind of research, I suppose because this practice would require little expense, therefore support for something that requires a little thought, instead of the many dollars for more expensive seed or chemicals. It looks to me that some universities may be better serving companies rather than the farmers.