Rust Mites & Twig Aphids

Just wanted to let folks know that I was in a field yesterday that had quite a few rust mites. It was up to our treatment threshold of 80% incidence and at least 8 mites per needle on one shoot. The most I saw was 25 mites on a single needle. So, it's not too early to get out there and look for rust mites.

I haven't seen my first twig aphid hatched out yet, but I'm sure they have started to hatch. Really, there aren't many fields that have much twig aphid in them. You might have to pull of 10 to 15 shoots before you find an aphid egg. Don't be fooled, though. That slight number is still enough to cause damage if we get a warm, dry spring. Of course, we haven't so far, so we might do well with twig aphids this year.

March Madness

Well. Not quite. I thought it might get people's attention. Of course, people do get a bit mad in the spring. "Mad as a March hare," the English used to say. People are just now realizing what all they have to do this spring -- at least I know I am.

Just wanted to share a few observations I and others have been making this spring.

BALSAM TWIG APHIDS: I haven't seen any hatched yet, but the eggs are getting plump like they are ready to hatch. However, I haven't found any fields so far with a high incidence of twig aphid eggs. You might pull off 10 shoots before you find an egg. I guess last spring it stayed so wet that the aphids didn't reproduce well. Remember, though, that even these low numbers can result in damaging levels of twig aphids if the spring is warm and dry, as the aphids reproduce so quickly.

VOLES: Both Bryan Davis and Doug Hundley are seeing greater than normal vole activity. With all the snow cover, it only makes sense.

Bryan sent the following in a March 17 email, "I have seen a tremendous amount of signs of rodent tunneling under the snow. During the winter when the snow melted on some fields signs were visible and as I've been out over the last two weeks I've thought this is the most sign I've ever seen. I recall seeing some signs of rodents last fall where we were spraying deer repellent and as I've returned to these farms there is more signs of rodent activity. The tracks I'm seeing don't seem to bee tunneling in the soil, but on top of the ground. I haven't seen any damage such as girdling or dead trees in these fields yet. I'm going back to one site today that has had a lot of activity and I'll look closer for signs of damage. As far as control, I had a grower asking about this last fall and I checked with Scott Henson about what they carry at CPS and they had rodenticides, but they came in large volumes. Hopefully now the hawks, foxes and cats can work on these pests."


I've only found voles damaging Fraser fir once -- and in that field they completely severed the trunks of small trees. The poor little trees looked like pencils stuck in the ground. Rodent control on that farm involved controlling the thick grass in the field, allowing the hawks to work it. Like Bryan says, the natural predators should take care of things.


RUST MITES: Bryan and I found some rust mites getting started over the last couple of weeks, but numbers were still very low.


OIL TRIAL FACTS AND FIGURES: Bryan sprayed some trees with the new Saf-T-Side oil last Friday. We used a backpack mistblower and a 2% rate. I'll try to get back there next week and see what the eggs look like. He was using about 100 gallons of water per acre to get good coverage. That is probably more than most growers could use, putting it out 3 1/2 gallons at a time. Another grower we talked to figured he was applying about 8 backpacks per acre for around 28 GPA.

That grower burned some trees with oil last year using his high pressure sprayer. All the needles fell off of some trees. The buds for 2009 weren't touched, and so all that's left is 2009 growth. Here is a picture of one of those trees. Hopefully this new oil will be easier for growers to use and won't cause burn.


Oil isn't cheap. If you are using the regular oils which are about $14 a gallon -- a 2% solution and 300 GPA comes out to $84 per acre. When Bryan sprayed last year, he used up almost a case of oil (5 gallons) on 1,000 trees which cost more than $100 per acre. But, Bryan hopes to market these trees as "pesticide-free" this fall which should give him an advantage over conventionally grown trees.


If anyone sees any interesting pest problems, let me know so I can share them with everyone.

Our Natural Stands

This picture was taken on Roan Mountain in the last few days. It's still another world up there -- a winter world even though everywhere else is starting to green up. I just wanted to let people see what Fraser fir and the native pests that affect them such as twig aphids, Cinara aphids, mites, and rosette bud mites are adapted too -- harsh conditions! So they can take the cold winter we've had this year.

EHS observations for early March

I was finally able to make it into the field on Monday! Of course, I had to nurse my sore knee through the wet snow and mud on slippery slopes, but I managed OK with the help of Bryan Davis and Jim Hamilton.

Anyway, I wanted to see how the elongate hemlock scales survived the winter. We collected scales from an area that has never been treated with any insecticides except Di-Syston. What I observed was that about 70% of the scales were dead. Most of the nymphs appeared dead -- 85% mortality. The mature female nymphs were surviving much better. Only 37% of those were dead and some females had eggs ready to hatch.

What will that mean for scale this year? It certainly was affected by the winter weather, but there is still plenty left alive to start all over again this year. Also, treating now for scales probably wouldn't do much, as the most resilient form, the adult female, is about all that's left.

Spring Insecticides for Pest Control

The weather so far this year has put many people behind already. Many growers treated last fall with insecticides and are hoping to get twig aphid control this spring from those fall sprays. In fact, in talking with county agents, we estimated that at least 4,000 acres of Fraser fir Christmas trees were treated in the fall and will hopefully skip a twig aphid treatment.

But what options do growers have that didn't treat in the fall? I'll try and list them all below. If anyone has any other's they'd like to share, email me and I'll add them. As I go through different materials, I'll be using abbreviations for pests with BWA=balsam woolly adelgid, BTA=balsam twig aphid, SSM=spruce spider mite, HRM=hemlock rust mite, and EHS=elongate hemlock scale.

The first consideration is do you even need to treat for twig aphids? If you aren't cutting out of the trees this year or next, you don't need to control BTA. You should walk through your trees to make sure mites aren't a problem, but you can probably skip treatments.

A second consider is what have you used in the past for insect control. It's important to rotate materials from different chemical families. In other words, products like Asana and Talstar are both synthetic pyrethroids and so have similar modes of action. Think about what you used in past years, and try to use other products this year. For a complete listing of all the chemical families, go to the IRAC Mode of Action Classification.

Another consideration is that it doesn't all have to be done in the spring. You can get control of pests in the summer and fall when you have more time and can pick better weather conditions. At the end of this post, I have some possibilities for when to treat if you have all the major pests.

And just a few more words of wisdom: Remember that all pesticides are dangerous to something -- whether the bees in your trees, or the stream insects below your field, or the man putting it out -- so read and follow the label. Labels can change every year, so be sure to read them each spring. Also, be considerate of your neighbors. Remember that getting good coverage is just as important as what material(s) you choose to use. Also remember that if the wind is blowing, or if it rains before the spray has dried, you are wasting your time and money. Be sure to scout after using any of these products to make sure they have worked.

Anyway, here is a list of products, their rates, different mixes and what they will control.

1. Horticultural oil. Use a highly refined oil -- 92% unsulfonated residues or better -- at the full 2% solution -- that is 2 gallons in 100 gallons of water. When applied in March with a high pressure sprayer, it will control BTA and HRM very well, and will help reduce SSM, BWA, and even EHS. Be sure to get good agitation so the oil and water don't separate. We're going to be looking closer at Saf-T-Side oil which won't separate in water to see how well that works.
2. Asana. Can be used anytime from February through bud break to control BTA (5 oz/100 gallons) and BWA (10 oz/100 gallons). Add a miticide if mites are present. Will also knockdown EHS. However, there is also a potential to create problems with HRM and SSM when using Asana -- even the following spring. If BWA control can wait until fall, rust mite problems can be avoided when using this product. 
3. Dimethoate. Use at full rate of 24 oz/acre. From last week of March through bud break will control BTA and knock-down EHS, HRM and SSM.
4. Dimethaote + Savey -- BTA plus SSM control (the Savey controls the mite eggs). Also Apollo can be used in this manner. Still will only knockdown EHS and HRM.
5. Di-Syston 15 G -- There might be some folks who are still using this. It will control BTA and SSM and possibly a brief knockdown HRM. Be sure to apply when there is no wind and scout after treatment to make sure it worked.
6. Talstar. Use at full rate of 40 oz/acre. Will give BTA and BWA control from February through bud break. Should also give control of SSM. (Though Talstar doesn't have any activity against mite eggs, it should last long enough to kill the mites that hatch from the eggs). Doesn't control HRM or EHS well.
7. Talstar + Dimethoate -- BTA, BWA, SSM and knockdown of HRM and EHS.
8. Thionex. Use at full rate of 2/3rds of a quart (about 21 ounces) for BWA control. Wait until mid April through bud break to get BTA control as well. (It just seems that BTA control is more reliable with Thionex if you wait until all the aphids have hatched out). Add a miticide if mites are present. Has no activity against EHS.
9. Thionex + Dimethoate -- BTA, BWA control and EHS, SSM and HRM knockdown. Some folks have been using this mix without scouting first, thinking that it will control about every pest. But control of mites and scales will only be fair.
10. Envidor. Use at 18 oz/acre for HRM and 25 oz/acre for SSM control. Therefore, if you add Envidor to any of these products listed above, you will also control these mites. Will it keep the mites from developing later in the year or next year? Probably not. I would prefer seeing people keep on scouting and apply when needed -- not as a preventative.
11. Dimethoate + Asana -- Use dimethoate at rate of 16 oz/100 gallons and Asana at the highest rate of 10 oz/100 gallons. Will control BTA, BWA, EHS and knockdown SSM and HRM. Wait as close to bud break as possible to get the most out of EHS control.This mix would give better control of EHS in summer.
12. Dimethoate + Prev-Am Use Prev-Am at 0.4% solution (50 oz/100 gallons). Will control BTA, EHS and knock-down of SSM and HRM. Prev-Am has burned trees at higher rates, so be careful, but this mix sure smells better than straight dimethoate!
13. Lorsban -- will control BTA and knockdown SSM and HRM (?). Will also control BWA in March -- but not once woollies start laying eggs. Will control EHS??? We're still looking at this, but it did a great job last October. We've seen some issues with Lorsban burning foliage, so be careful.

So, what would I use if I had everything -- BWA, BTA, SSM, HRM, and EHS? I would probably either use Asana + Dimethoate and continue scouting for the mites to see it they rebound, treating with Envidor if they do, or go ahead and use Asana + Dimethoate + Envidor (which would be rather pricey). Or, I might wait to control my BWA and EHS in the summer with Dimethoate + Asana, and just use dimethoate in the spring -- and scout for mites later on. If you wait until August or September, you should pick up BTA control for the following year. Or I might use oil in March every year to control all these pests.

Beating Trees to Beat Bugs

SUMMARY: To decide what insecticides to apply in the spring, it is important to scout in April to determine if twig aphids and mites are present in a field. Use foliage beats for twig aphids and examine shoots for rust mites and spider mites. Always use a hand lens. Though scouting takes time, it will end up saving both time and money by helping to determine exactly what pesticides, if any, are required.


I finally made it to Ashe County yesterday. It was good to at least make it into Christmas tree country again. I saw several blue birds which is always fun.

Bryan Davis and I chatted with some growers who had treated different blocks of trees with Dimethoate + Asana at different times -- anywhere from the end of June through mid September. They wanted to know if they had controlled the elongate hemlock scale and if they could skip twig aphid treatments in the spring. It will provide us a great opportunity to evaluate different timing of these materials for both scale and twig aphid control. After all, most of the fall treatments that have been followed over the last several years have been with Talstar, not Asana. It will be interesting to see under different conditions how well the Asana performed. But our conversation also made me realize what all growers will be facing this spring.

Of course it's so snowy, you can't even get out in the field now, even if you could tell anything about pest control. If you can make it to the field, there is a layer of ice on the snow that makes walking difficult. People are sitting around knowing they are already getting behind this growing season before it even gets started. In the spring, growers need to plant, fertilize, get herbicides out and insecticides. Some even have a bit of shearing that needs finishing. I'm afraid, scouting may be one of those things that doesn't end up getting done.

How do you get it all done when you don't have the time? Fortunately, scouting doesn't have to take a lot of time. The two most important pests a grower needs to evaluate in the spring are twig aphids and rust mites. Neither should take a lot of time to assess. As pictured with this post, taking beats of foliage on just a few random trees in each block will let you know if fall treatments with insecticides have controlled twig aphids. Start this in mid-April.

This photo shows a beat with a lady beetle larvae (the big bug) and four twig aphids (one fairly big and three small). Always use a hand lens when you look at what fell out. If you find more than a couple of trees with twig aphids, you will need to treat again in the spring. At the same time when you look for twig aphids, pull a few shoots and look with a handlens for rust mites. If there are only a few, make a mental note to check again in a few weeks to see if the numbers are increasing. Remember that rust mites are very small. If you are just looking at foliage beats, you'll miss finding all but the heaviest populations of rust mites. By taking both foliage beats and pulling shoots, you will also learn if spider mites are a problem.

The fields I mentioned earlier that had had Asana in the summer or fall are much more likely to have rust mites this spring -- but there's no reason to assume mites will cause enough damage to worry about. The earlier the Asana was applied, the more of a problem rust mites are likely to be, so we advised the growers to scout those fields first. But if this spring stays fairly cold and wet, rust mites might never become a problem. As I start getting out in the field in March, I'll let everyone know in this blog what this spring looks like as far as rust mite pressure in general.

Unfortunately, some growers seem to be skipping scouting, and just treating everything in the spring with Dimethoate + Thionex, thinking that these two materials will control everything. After all, Dimethoate will control spider mites, rust mites, twig aphids and some scale, and Thionex will control twig aphids and woollies, and neither is that expensive. But remember, Dimethoate's control of mites can be short lived, and Thionex gives no added help with scale control. Twig aphid control with Thionex has been variable, and we're not sure why. These are also the two most toxic insecticides that growers use, and they also smell really foul, making them an issue with neighbors. And why spray anything at all if you don't need to? If you treated last summer and fall, you might not need to treat again this spring. And even if you didn't, twig aphids and mites aren't always a problem every spring.

Scouting takes time, but it also saves time, money and pesticides. If you aren't confident about scouting, call Extension for help. There are also scouts working in the counties that can be hired to do your scouting for you. For their names, call the County Extension Agents in some of the bigger tree counties.

I hope to get out to the fields we talked about yesterday and some I treated last fall starting the second week in March. I'll let you know what I find. In my next post, I'll go over some of the pesticides and timing that can be used for pest control this spring. But remember in April, to take your beat sheets (white plastic plates work great --thanks for that tip Doug Hundley!) and hand lens with you.

If You're Missing Di-Syston...

SUMMARY: If you are treating for twig aphids this spring, there are many choices available both in pesticides and spray equipment. It is not necessary to treat trees for twig aphids until two years from harvest. Larger growers are using tractor-driven airblast mistblowers. For smaller growers, a backpack mistblower is a great alternative.

Many folks have started spraying in the fall for Cinara aphids and balsam woolly adelgid, which frequently results in twig aphid control the following spring. If you aren't one of those people, you will probably need to treat for twig aphids this spring.

Twig aphid control is only important the year of sale and year before sale. There is no need to control twig aphids in younger trees, as the new growth will hide the needle curl. If there is damage and even reduced growth, the trees tend to set extra buds for the following year, and growth will not be slowed down at all. But if it takes 2-3 years to harvest all the trees out of a block, a grower may end up treating 4-5 years in a row for twig aphids.

Traditionally, people treated right before bud break. Since most were using the granular formulation of Di-Syston, this was the a good approach as it was important to wait until all the eggs had hatched. This product is no longer available for use and other products can be applied much earlier in the spring.

The loss of Di-Syston will especially impact the smaller growers who may not have spray equipment. Most larger growers have switched more and more to using tractor-driven airblast mistblowers as the price of Di-Syston increased during recent years. This equipment gets good twig aphid control provided there are enough access roads. Adding a material to the pesticide to increase droplet size is helpful to both reduce drift and get better coverage. Be sure to scout in the middle of the block after April 15 where coverage may have been light to make sure control is adequate. But if you don't have a mistblower, you will need to decide how you will treat in the spring.

A high pressure sprayer is always the best choice for pesticide application as you will get the best coverage. For twig aphid and mite control, it is not necessary to crank up the pressure or use a straight-stream spray pattern as you would with balsam woolly adelgid control. Instead, reduce the pressure, broaden the pattern, and you will find you will get better foliage penetration. Don't try to treat more than 2-4 rows at a time, even in smaller trees. Unfortunately this application method is slow, and smaller growers often can't afford these sprayers. If they hire someone else to spray their trees, and the weather doesn't cooperate, they risk not getting their trees sprayed at all.

If you are a smaller grower, a backpack mistblower may be the answer. This equipment gives enough coverage to control all Fraser fir pests including woolly adelgid. It gives much better coverage than a regular backpack sprayer. There are several lower acreage growers that only use this to apply insecticides. The sprayer is not for the physically weak! It is heavy, but even I can handle it on steep ground. It sprays faster than I can walk, but you can change the settings to reduce spray output. And priced between $600-700, most growers can afford it. You will find you will apply around 50+ gallons of water per acre which means a lot of trips to fill up, so having a nurse tank is helpful.

Whatever equipment you use -- mistblower, backpack mistblower, high pressure sprayer -- be sure to treat trees from opposing directions. Try spraying some trees with plain water to make sure you are getting good coverage. And DON'T TRY TO SPRAY WHEN THE WIND IS MORE THAN 10 MPH or IF IT'S ABOUT TO RAIN. It's just a waste of pesticides, time and effort, and makes the entire industry look bad.

There are many choices in pesticides for spring pest control. I'll go over these in another post. But remember, for many of them you can spray beginning in March -- which is just next week! (Guess we'll have to get rid of the snow first!) Don't wait until the last minute as you never know if the weather will allow you to spray or not.