Think Out Loud

How grasshoppers and drought affect Oregon ranchers

By Rolando Hernandez (OPB)
May 6, 2022 4:26 p.m. Updated: May 13, 2022 8:38 p.m.

Broadcast: Friday, May 6

Cattle graze on an irrigated pasture near Ft. Klamath. New rules will prioritize stock water, but not irrigation water, for ranches during a drought in the Klamath Basin.

Cows graze on farmland on a sunny day. As drought conditions continue, favorable conditions for grasshoppers could mean another outbreak.


Oregon’s drought-stricken lands provide optimal conditions for grasshoppers. Last year, the state saw one of the worst outbreaks in the past 50 years. Grasshoppers, and other insects like Mormon crickets, are feeding on already low supplies of forage and many ranchers are working with less water. As the drought continues, some are worried what insect populations will look like this summer. Ian McGregor is an assistant professor at Oregon State University’s College of Agricultural Sciences. He joins us to share what ranchers faced last year and what can be done to deter another outbreak.

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Note: The following transcript was computer generated and edited by a volunteer.

Dave Miller: From the Gert Boyle studio at OPB, this is Think Out Loud. I’m Dave Miller. We have talked a lot about drought over the last few years, about wildfire danger, and salmon, and plunging aquifers, and a lack of water for irrigators. We turn now to yet another knock-on effect of the drought. It turns out that parched lands provide optimal conditions for insects like grasshoppers and mormon crickets. In fact, last year Oregon saw one of the worst infestations in the past 50 years. That’s yet another problem for farmers and ranchers. Ian McGregor is an assistant professor in the College of Agricultural Sciences at Oregon State University. He joins us with more. Ian McGregor, welcome.

Ian McGregor: Hi, thanks for having me.

Miller: Thanks for joining us. Why do grasshoppers thrive in droughts?

McGregor: I’m not exactly sure. I think it provides the environmental conditions that promote hatching rates and then the larva coming out of the ground, something along those lines. That’s just my best guess, but I don’t have a validated scientific argument for that. But there is some literature that does show that grasshoppers do tend to come out in higher numbers in drought years.

Miller: It has been a very rainy spring in the Willamette Valley. More snowpack in the Cascades. Has that translated at all to Central and Eastern Oregon?

McGregor: So that’s a great point that you brought up. I was having this conversation earlier about how here in Klamath County this day in May last year, if you were out in a pasture and you lit a match or something, it would have been a serious issue, because this time last year we were very hot and dry. However, with this spring precipitation, it’ll be really interesting to see what happens in terms of grasshopper rates across the state. With this extra moisture, it might actually suppress some of those numbers. We’re learning as we go along, and I think this year will be a great learning experience, but it’s definitely different than last year because this time last year we did not have this moisture.

Miller: Can you give us a sense for how bad last year was, or the year before, in terms of grasshopper infestations?


McGregor: It was all across eastern Oregon. I’ll start by throwing out some numbers. So say you have 6-7 grasshoppers per square yard, across 10 acres, you have enough grasshoppers in that area, they eat as much forage as one full grown cow. And I believe if you increase that to 17 grasshoppers per square yard, I believe across 40 acres, they’re eating one ton of forage every day. And last year we were seeing grasshopper infestation levels across eastern Oregon at a point where there were too many to count. It was described as carpeting the ground and [voice noise in background] . . . so sorry about that . . .

Miller: That’s alright, you exist as a physical body in an office somewhere.

McGregor: Yeah, I’m in a high school, they’re making announcements. Anyway, we had grasshoppers literally carpeting the ground last year. And it was pretty sad, frustrating situation for me, because I had a lot of calls from producers who woke up one morning and the crop that they just invested a bunch of money in, it gets turned into a parking lot. They just completely take everything and move on to the next field. And that last year was devastating. And during a drought year, you’re thankful to have the little amount of forage that you do have. The grasshoppers just came and took it away. Yeah, last year was a really tough, difficult year in terms of grasshoppers.

Miller: Are grasshoppers something that are always a problem? And the issue here is that during a drought, they can become a mega problem or are they sort of a novel issue for these ranchers or farmers?

McGregor: I think it’s an infrequent issue. Most years, you’ll see grasshoppers around every year. And in most years they’re present at numbers that don’t, cause much of a problem. And grasshoppers are great for the ecosystem because they’re an essential part of the food web. But grasshoppers have been occasionally a huge issue for a very long time. And yeah, it seems that there is some correlation with really dry hot years, where we have them in numbers, where it’s a legitimate issue.

Miller: So because of all this, as an assistant professor of agricultural sciences at OSU, you have been trying to teach farmers and ranchers over the last year about some management ideas of how to respond to this. What options do people have?

McGregor: So I’ll start with this: there’s a window of opportunity here. Last year I was on a ranch with some local partners and ranchers, and we were talking about something. And this was this time last year, and we were kicking around the dirt, and I was like ‘hey it’s a dry year. Data shows that in dry years, grasshoppers can be a huge issue.’ And it seemed to get shrugged off at the time, because the grasshoppers were not right in front of us.

Miller: Meaning the ranchers that you were talking to were shrugging you off?

McGregor: Yeah, because it’s a difficult thing to really take seriously unless the grasshoppers are right in front of you. I don’t blame them for that. But it was maybe a few weeks after that where everybody was like ‘holy cow, we need to do something about this grasshopper issue.’ Well, the issue is, I believe it’s after the third or fourth instar, any kind of management solution you want to implement is basically useless after they get to that level of maturity, and especially once they develop wings, because they just fly everywhere.

Miller: Just one second. I bet I’m not the only person listening who doesn’t know what the fourth or fifth instar is.

McGregor: So instar is just basically a word that translates the stage of maturity of the grasshopper. And so anything beyond the fourth instar is going to be a fully grown adult grasshopper and before the fourth instar imply different physiological stages of the grasshopper. And so if you’re below four then it’s a larva or it’s just starting to develop its more mature body parts.

Miller: So basically it totally does. Basically by the time the ranchers were getting back to you saying, ‘hey you may you may not have thought of this, but we’re having a grasshopper problem’, you said it may be too late for you now?

McGregor: Management, no matter what you’re doing, it always costs money or time and so you don’t wanna waste that money or time doing something that’s gonna be ineffective. There’s some scientific literature that suggests that grasshoppers, the rate at which they mature through these different instar stages, is driven by thermal accumulation, which can be calculated and quantified by using growing degree days. The literature shows that grasshoppers start to emerge from the ground at around 150 growing degree days. And then there [were] also growing degree days that correlate to the different instars of development. I believe in Klamath County we hit 150 growing degree days, not too long ago. And so there’s this window of maybe 3 to 4 weeks, depending on the climate and everything, where management is effective. I’ve been working with producers, I’ve been tracking growing degree days. As we’ve been approaching this 150 growing degree day mark, I’ve been calling people to just make sure to keep a lookout for things, maybe do some scouting to see if they’re seeing any grasshoppers. And again, with the spring moisture, whether it’s gonna be a horrible infestation this year or not, is still in question. But we’re making sure that being preemptive about this, and making sure producers have their ducks in a row, so that we don’t miss the mark. And another important thing is that if one property owner practices some kind of suppression method and then the other neighbor does not, well, the grasshoppers fly and then it basically renders that one landowner’s efforts useless. And so we’re trying to work out a system where we can get all the neighbors on board in these susceptible areas, and try to figure out a system that’s effective. So I think that would be the biggest chunk of actually addressing this issue in an effective way.

Miller: Ian McGregor, thanks very much for joining us today.

McGregor: Hey, thank you as well. You have a great day.

Miller: Likewise. That’s Ian McGregor, Assistant professor of Agricultural science at Oregon State University.