Monday, August 31, 2015

Rumors of Sugarcane Aphid Resistance and Adaptation to Corn Are Unsubstantiated

Dr. Ed Bynum has addressed some unsubstantiated rumors flying around the High Plains; 1) that sugarcane aphid has become resistant to insecticides in Mexico and 2) that it is now able to develop on corn and is damaging corn in Mexico. I tried to address this last topic in my post last week, but Dr. Bynum has provided more detail on both issues in his newsletter post today.

The bottom line is that there is no evidence of insecticide resistance and no evidence that the aphid can damage corn.

Friday, August 28, 2015

Corn, Cotton and Sugarcane Aphids

Many people on the High Plains are finding what looks like sugarcane aphids on corn and to a lesser extent cotton, and the question we are receiving is whether the aphid will get on these crops and, if so, will it become a problem.

The answer to the first part is a definite YES; they will get on all of our plant species. In the past few weeks we have had billions of winged adults flying from sorghum fields and all of them need to land somewhere. They are basically like flakes of ash from a giant volcanic eruption and will settle out over the landscape.

The answer to the second part of the question is that neither corn or cotton is a good host for the aphid. Small aphid colonies are being found on these crops but they are not expanding rapidly and will not get anywhere near pest status, at least if our aphids behave like sugarcane aphids do in Mexico and south Texas. Sandy Endicott from DuPont Pioneer monitors the sugarcane aphid situation in Mexico and the southern U.S. and provided some perspective to us earlier in the week. In Central Mexico there are four counties where the sorghum crop is a complete loss. The report went on to state that DuPont Pioneer people were finding small colonies on corn, but that there was no concern at this point but they will continue to watch closely. The situation on sorghum in Mexico seems to be extreme yet only small colonies are being found on corn. This matches what our Extension Entomology colleagues Danielle Sekula-Ortiz and Raul Villanueva have reported from the Valley; small colonies only and these do not persist. Corn, being a grass, is much more closely related to sorghum than is cotton, a dicot. The sugarcane aphid has adapted to sorghum and its relatives (including millet) but not to corn, and certainly not to cotton. (Cotton aphids, which look quite similar to sugarcane aphids, are currently being found on southern High Plains cotton.)

Having said all of this, aphids are good at adaptation if they have the genetics to do it. As far as we know, and based on a lot of credible information, none of our crops that are not in the sorghum group are at risk. We would appreciate reports of healthy looking and expanding colonies of sugarcane aphids on any of our non-sorghum crops. Our contact information is here. We don't expect any phone calls but it never hurts to be vigilant.

Sunday, August 23, 2015

Headworms Up; New Invasive Aphid Found in Panhandle

Headworms and Late Corn Fall Armyworm

Corn earworm and fall armyworm adult trap captures are up significantly in the last week and this means headed sorghum should be scouted for headworms. It also means that late planted non-Bt corn should be scouted for fall armyworm. Corn earworm is not an economic problem in corn, but fall armyworm can do a lot of damage to ears if it infests them prior to hard dough stage. Prevathon and Belt are good choices for control of fall armyworm in corn and they will not flare spider mites (which are also being found readily in corn and sorghum). As headworm insecticides they will not flare sugarcane aphids in sorghum. 

New Invasive Aphid Pest

Sipha maydis, which we are choosing to call the hedgehog aphid after Colorado State University's lead, was found in Lipscomb and Hockley counties on sorghum on the same day last week. Given the distance between discoveries it is likely that the aphid is widely distributed on the High Plains and we would appreciate reports of new discoveries. 

The aphid is easy to recognize; it is shiny black with white spines.

Dr. Ed Bynum has written an excellent summary of what is known about S. maydis in his newsletter. This pest of small grains has the potential to be a serious threat to wheat and other crops. 

Friday, August 14, 2015

High Plains Sugarcane Aphid Thresholds Lowered

Experience with the sugarcane aphid in the last few weeks has prompted us to lower our treatment thresholds. The new thresholds can be found on our Sugarcane Aphid News website. The article concludes with suggestions for tank additives for sugarcane aphid control. 

Tuesday, August 11, 2015

Spider Mites in Sorghum

Dr. Ed Bynum, Extension Entomologist in Amarillo, has published a good summary of the spider mite situation in sorghum this year. I have seen some fairly heavy infestations in fields but don't have time to write. And Dr. Bynum's article is better than I could do anyway.

Spider Mites in Sorghum, Texas Panhandle Pest News, August 11, 2015. 

Wednesday, August 5, 2015

Multiple Aphid Species in Sorghum, What a Year

Some area sorghum fields are experiencing significant numbers of aphids, but not just sugarcane aphid the recently arrived pest from the south. We also have high numbers of yellow sugarcane aphid, greenbug and corn leaf aphid. Of these, the corn leaf aphid is the only one that is not a threat.

Blayne Reed, Ed Bynum and I put out the first sugarcane aphid control experiment today just east of Hale Center. The pre-treatment count averages were something like 70 sugarcane aphids per leaf, 60 yellow sugarcane aphids and 30 greenbugs. (I have not formally tallied the numbers yet, but these are best guesses from my tired brain.)

Dr. Bynum wrote an excellent article on the practical and important differences between sugarcane aphid and yellow sugarcane aphid, and it can be found here. He discusses biology, damage and thresholds.

As you scout fields be sure to note the number of sugarcane aphids, yellow sugarcane aphids and greenbugs separately. As Dr. Bynum notes in his article, we don't have any thresholds for yellow sugarcane aphids on older sorghum so we recommend spraying them on the greenbug damage thresholds. However, if there are a significant number of sugarcane aphids in the field then it would be a good idea to treat the field with an insecticide that took out sugarcane aphids. These insecticides, Transform and Sivanto, are also effective on yellow sugarcane aphid and greenbug. However, the reverse is not true; our traditional insecticides for yellow sugarcane aphid and greenbug are not very effective on sugarcane aphid. So spray to kill all three species - don't leave sugarcane aphid in the field.

Sunday, August 2, 2015

Good News: Fall Armyworm Not Numerous

It has been a very strange summer; early indications pointed to a bad fall armyworm year, but trap captures in that last two weeks suggest that we might get a break. As the graph above shows, fall armyworm trap captures at Lubbock are well below the three year average. Kendra Bilbrey, Cochran County Extension Agent, has also been operating fall armyworm traps and her data agree with the very low fall armyworm moth numbers found at Lubbock. 

Kendra Bilbrey's fall armyworm trap data from Cochran County. 

This is great news for sorghum because fall armyworm is part of the headworm complex. Corn earworm (cotton bollworm) is the other part. I don't have trap data for corn earworm, but my field sampling tells me that the numbers are around normal. Additionally, late planted corn that is entering green silk stage will draw corn earworm and fall armyworm away from sorghum. Green silk corn is highly attractive to these insects and neither of these pests can tell whether the corn on which they are laying eggs is Bt or non-Bt. In essence the late planted corn will act as a trap crop and provide partial protection for nearby sorghum. This is not necessarily bad news for corn; Bt will kill many of the caterpillars. 

However, late planted non-Bt corn might be in for a rough time; it will attract these late summer fall armyworms and corn earworms. This is one of the reasons that non-Bt corn should not be planted late on the Southern High Plains, and it is one of the reasons that, in an earlier post, I hinted that late planted corn should forego the required non-Bt refuge this year. The real worry in corn is fall armyworm rather than corn earworm, and the fact that fall armyworm numbers are well below average right now is a good thing for all of the late planted corn in the area. 

So, at least for right now, the indications are for a relatively light headworm year in sorghum. And this is the year we really need it! Headworm insecticide applications with the usual products could flare sugarcane aphid. (There are two headworm products that won't flare sugarcane aphids; Prevathon and Belt.) A three axis threat to sorghum; sugarcane aphid, sorghum midge and headworms, could be an expensive proposition. But at least for right now it looks like the headworm part of the equation won't amount to a serious problem in the next few weeks. Of course I don't have a crystal ball and am not going to make any assumptions about late planted sorghum; corn will not be attractive for egg laying past green silk stage and thus sorghum might get heavier infestations. But for now I will take a little good news and we will keep tabs on what happens in the next few weeks. 

Saturday, August 1, 2015

Getting Ready for Sorghum Midge

In the July 8th edition of FOCUS I promised to write more detailed information on sorghum midge. This year a lot of sorghum was planted earlier than normal in order to avoid the potential worst problems associated with sugarcane aphid. (Congratulations if you employed this IPM practice! It seems to be paying off now that sugarcane aphid is firmly established in Southern High Plains counties.) In general, sorghum that completes bloom before August 4th or so in our part of the Southern High Plains will escape economic midge damage. However, some of this early sorghum and the abundant Johnsongrass can serve as early hosts for midge and give later populations a head start. It is too soon to know what midge populations will be like this year, but on balance we have plenty of egg-laying hosts in the system.

As I started this article I saw an excellent summary from Angus Catchot and Jeff Gore at Mississippi State University. This article is so good that I am going to link to it as most of what I would have written about sorghum midge: it contains recognition, biology, scouting information and control suggestions: http://www.mississippi-crops.com/2015/07/18/scouting-for-sorghum-midge-with-confidence/ .

One key point about sorghum midge is that it lays eggs in blooming sorghum only on the day the anthers are visible. However, it takes several days for a sorghum plant to flower from the top of the panicle to the bottom and, due to uneven flowering across the field, it may take a week to ten days for the field to complete pollination. Adult midges (tiny flies) live about one day, but there is continual re-infestation of the field each day, so low midge numbers on the first day of flowering might be high midge numbers in subsequent days. And overall midge numbers in the system increase as August progresses.

Sampling should be done in mid-morning, or after temperatures have reached 85 degrees. The treatment threshold depends on sorghum panicles per acre, midges per panicle and cost of control. The threshold calculations can be found in Managing Insect and Mite Pests of Texas Sorghum on page 19 - 20.

Insecticide selection has changed because sugarcane aphid is present in many area sorghum fields. Our management recommendations prior to sugarcane aphid were pyrethroids, Lannate, Malathion and Lorsban. Unfortunately, all of these insecticides kill beneficial insects, the same insects that help slow down the sugarcane aphid. And, to make matters worse, they don't do a good job of killing sugarcane aphids. So the net result of using them might be to help sugarcane aphids rapidly increase in the field. However, it is important to treat midge if it reaches threshold; do not forsake a needed midge treatment out of fear of what might happen with sugarcane aphid.

As a practical matter, scout the field carefully to determine whether there are sugarcane aphids present. If so then you can still use the insecticides listed above, but consider adding Transform or Sivanto for sugarcane aphid if you think you need to. Or be prepared to come back with Transform or Sivanto later. Not all midge insecticides will risk flaring sugarcane aphid; Blackhawk has just received a 2ee label on sorghum for midge control and should be used at 1.5 - 3.0 oz per acre. I do not have direct experience with this spinosad product, and in fact have not seen the new label, but Dow says is will work and they stand behind its performance for full control.

I am not sure that we will have an increased midge problem this year, especially since all bets are off due to the very wet spring and early summer. However, I wanted to provide some information on making midge control decisions in light of sugarcane aphid.

Sorghum midge: Patrick Porter