With the holiday season over, it’s time to turn our attention to Spring bedding crops. Although here for a brief window, the diversity of these crops means you’re bound to encounter some sort of disease and insect problems.
One way you can head off issues is to plan and prepare now. This post has important tips on sanitation for common spring crop diseases, dipsandearly sprays to prevent key pests, as well as tips on where to spend your biocontrol dollars.
Investigating biocontrol options for our industry is always important, given the lack of registered insecticides in this country. Currently, we are relying heavily on two closely related chemicals – Beleaf (flonicamid) and Endeavor (pymetrozine) – for control of the foxglove aphid (Aulacorthum solani). If our battle with thrips (and Bemisia whitefly) have taught us anything, it’s to be prepared for chemical failure.
Unfortunately, biological control of foxglove aphid has been challenging so far. For example, my own research showed that Aphidoletes, a “generalist” aphid predator, actuallyhas lower preference for foxglove aphid than other species, and is less effective for this pest. However, a long-term project by Dr. Michelangelo La-Spina (Vineland Research and Innovation Centre) has found some results that get us closerto being able to control foxglove aphid WITHOUT resorting to pesticide sprays.
You know the old rhyme: “April showers bring May flowers, but what do May flowers bring? Aphids“. Or sometimes it seems that way, anyways, with Spring bedding crops.
To help guide your pest management program this year, our friends (superiors?) over at Michigan State Extension have released a handy list of which crops are likely to attract which pests. Keep reading for more info.
Aphis gossypii come in a variety of colors, as shown above. But all colors share one thing in common – black cornicles at the tip of their bodies. These can be seen with a hand lens.
Usually on this blog we bring YOU the information. Today it’s the opposite. I’m looking for a grower who has live melon aphid (Aphis gossypii) in their operation, and wouldn’t mind a researcher coming by to remove some of them to start a research colony with.
If you have some you wouldn’t mind parting with, please contact Rose Buitenhuis at 905.562.0320 Ext. 749 or email@example.com who can get in touch with our contact at Laval University. They might even name the colony after you…
As a refresher, Melon aphids tend to be the smallest aphid found in your greenhouse. They can come in a variety of color morphs – from pale green-yellow to dusky grey – but they ALWAYS have black cornicles (or “tail pipes”) at the end of their abdomen. They are common in crops like kolanchoe and gerbera and a variety of other spring crops.
If you comment on this blog post regarding aphids in your greenhouse only I (sarah) will see it.
Foxglove aphid feeding on pansy. Note the two dark-green spots on the abdomen and the dark leg joints which are characteristic of this pest.
Now that temperatures have cooled down, it’s time to start watching for foxglove aphid as your primary aphid pest, rather than green peach or melon aphid. Here’s links to 2 articles that were published this week that talk about this pest’s biology and control measures.
It’s that time of year again, when baskets of Million Bells (Calibrachoa) are going up in the greenhouse. Here’s how to deal with and prevent some of their most common issues.
Iron deficiency in Calibrachoa. The resulting yellowing can look similar to symptoms caused by black root rot or nitrogen deficiency.
From a nutritional standpoint, the best thing you can is keep the pH of your calibrachoa in its ideal range; between 5.5 and 6.0. A pH higher than this can inhibit nutrient uptake, especially micronutrients such as iron.
Iron deficiency can be difficult to distinguish from other issues (like Black Root Rot – see below), but typically leads to yellowing of new growth. Leaves may only show chlorosis between the veins, or it may be spread throughout the leaf. This is different from nitrogen deficiency where yellowing occurs in the oldest leaves. If iron deficiency occurs, adding a chelated form of iron is best for uptake.
Yellowed plant growth (yellow circle) and dead plugs (orange circle) on a plug tray of Callibrachoa from black root rot.
Million bells are also highly susceptible toBlack Root Rot (Thielaviopsis) – I’ve seen this take out a good chunk of a crop. Symptoms include:
Stunting of foliage and roots
Plants in a tray will have uneven heights
black areas on roots
yellowing of leaves
Prevention is worth a pound of cure with this disease, as it is difficult to eradicate once established. Important steps to take include:
Proper Sanitation. To avoid an issue with Black Root Rot year after year, immediately dispose of diseased plants, limit water splashing, and sanitize benches, floors and used pots/plug trays. Always physically wash surfaces with a cleaner to remove organic matter, then follow up with a disinfectant such as KleenGrow (ammonium chloride compound).
Consider prophylactic applications of fungicides onplug trays. Products include Senator (thiophanate-methyl) or Medallion (fludioxonil). Preventative applications are an especially good idea if you’ve issues in the past. Adding bio-fungicides containing Trichoderma harzianum(e.g. Rootshield, Trianum) may also help.
Lowering your pH. This diseaseis significantly inhibited by a lower pH – between 5.0 and 5.5.
Manage fungus gnats and shoreflies, since these insects can spread Black Root Rot between plants. Treatments include nematodes, Hypoaspsis mites , or applications of Dimiln (diflubenzuron) or Citation (cyromazine).
If already established, rotated applications of Senator and Medallion may limit Black Root Rot, but are unlikely to cure it.
Aphids tend to be found on flowers and new growth of Calibrachoa.
Lastly, Million Bells are highly attractive to aphids. With baskets hung up in the greenhouse, they can be “out of sight, out of mind”, but regular monitoring is needed to prevent large aphid outbreaks. Place sticky cards directly in baskets, and routinely check plant material for aphid cast skins and honeydew.
Once aphids are detected (and they will be!), applications of Beleaf (flonicamid), Enstar (kinoprene) or Endeavor (pymetrozine) will usually take care of them. However, be aware that all of these insecticides take around 4-5 days to start causing aphid death.
The spring bedding crop season is over, so now’s the time to reflect on what worked, and what didn’t, for foxglove aphid control. This way we can prepare for their re-appearance in the fall.
Foxglove aphid feeding on pansy. Note the characteristic dark-green blotches on the abdomen, and the dark joints of both the legs and antennae. Photo by S. Jandricic, OMAFRA.
To recap, foxglove aphid (Aulacorthum solani) is a “cool weather pest”. It prefers temperatures between 15-25 C, and can’t survive in the greenhouse in summer (1). Unlike other aphid pests, foxglove aphid tends to feed in hidden locations – primarily the lowest leaves of plants – making it difficult to detect and treat.
And, unlike green peach and melon aphid, biological control of foxglove aphid is definitely a challenge.
Some growers and consultants have been trying both Aphidius ervi and Aphidius matricariae for foxglove aphid. But, as demonstrated by the Buitenhuis Lab here at Vineland, foxglove aphid is a terrible host for A. matricariae, and this wasp will barely parasitize it (see graph). Further, using A. matricariae for foxglove aphid can actually end up spreading this pest, and it’s damage (2). This is because the wasps simply pesters the aphids to the point where they drop of the plant and go find a quieter place to eat. So it’s pretty clear that releasing A. matricariae is simply a waste of money and effort if you’ve got foxglove aphid.
Parasitism rates of foxglove aphid by different Aphidius species. Wasps were offered 50-60 2nd instar aphids. Tests were done in small plastic containers.
But what about A. ervi? Although parasitism rates were high in the lab (73%), results were not as good in practice. Tested in the greenhouse, A. ervi was able to offer about 50% control of foxglove aphid after 1 release.Repeated releases may offer greater control, but this is still not reassuring when you’re talking about a pest where populations can explode quickly.
Why A. ervi does a great job of parasitizing foxglove aphid the lab, but not the greenhouse, is something we’re currently investigating. But until we have an answer, it seems that pesticides may currently be the best option for control of foxglove aphid in floriculture IPM programs. With the current limitations on neonicotinoids, growers will want to turn to Beleaf or Endeavor. (But, since these two chemicals have similar modes of action, and it usually takes several sprays of either to provide complete control, you may want to consider rotating these chemicals with Enstar II to prevent resistance).
If you’ve had infestations of foxglove aphid in your greenhouse, and have anything to say about it’s control, feel free to leave me a comment!
(1) S.E. Jandricic, S.P. Wraight, K.C. Bennett, and J.P. Sanderson. 2010. Developmental times and life table statistics for the aphid Aulacorthum solani (Hemiptera: Aphididae) at six constant temperatures, with recommendations on the application of temperature-dependent development models. Environmental Entomology 39(5): 1631-1642.
(2) L. M. Henry, J.A. Bannerman, D.R. Gillespie2, and B.D. Roitberg. 2010. Predator identity and the nature and strength of food web interactions. Journal of Animal Ecology doi: 10.1111/j.1365-2656.2010.01723.x.