Root Aphids and Bonsai

A number of people here in the Northwest US have seen root aphids on both Yamadori pine and junipers collected from Colorado to Washington State -- and I imagine that the issue is not confined to these locations.

They are nasty little buggers and not easily killed. Discussions with local ornamental nursery professionals indicate they have the issue as well with some of their stock. The nursery trade appears to use rather nasty chemicals to rid their stock of these pests. However, these chemicals are not to be used lightly for bonsai, both from a cost and safety standpoint, and there are indications also they may harm bonsai if not carefully and properly used.

Research are Oregon State University a while ago indicated that these pests were killed 100% with a hot water immersion of the soil containing them at temperatures of 115 -120 F for periods of 5 - 10 minutes and the immersion did not damage the vine stock. Their work related to removing phylloxera (root aphids) from grapevine stock in the wine industry (reference: Title and Authors : Phylloxera in Oregon Grape Vines: Biology and Treatment of Planting Stock With Hot Water Dips Bernadine Strik and Paula Stonerod Associate Professor and Research Aide, Dept. of Horticulture Oregon State University.

Further , if you google “killing root aphids with hot water” a rather impressive number of posts come up indicating that the recently legalized cannabis industry is suffering from these little buggers also, and a numbers of growers have had success using the hot water dips of their growing product to get rid of the aphids.

I am wondering if anyone out there is familiar with this issue, and tried this technique (successfully) for bonsai? One important question which immediately arises is that of plant root susceptibility to water temperature -- and while there are MANY articles’ on root death from cold weather, there appear to be few if any on the impact of 120 F temperature water on bonsai plant roots – my interest is primarily for roots of junipers and pines, but also in the general effect of such temperatures for rather short periods (5 – 10 minutes) .

Jonas Dupuich had a pair of recent posts on root aphids in his blog Bonsai Tonight. http://bonsaitonight.com/2015/09/01/drench-for-root-aphids-follow-up-1/ is the most recent. He used a variety of insecticidal drenches on different groups of seedlings. I had a pair of pines that were yellowish for no good reason and used one of the drenches (a small amount of Imidacloprid I had left). Both seme to be doing better in my case - one greened up a bit and the other set the best buds it has had for a couple of years. I too look forward to hearing about the hot water treatment for pines and junipers because there are definitely fewer environmental and personal hazards with 46 - 49C water.

I am not exactly sure we are talking about the same buggers or not, but I have treated Bald Cypress for root aphids with Orthene ant killer with success.

It typically takes a couple treatments over the course of a few weeks. I sprinkle the powder on the surface of the container and then lightly water in. In extreme case I have removed the tree and also sprinkled on the underside of the root mass. Repeat in 2-3 weeks.

120 degree water seems a little scary to me( a quick search says that 120 degrees with scald your skin with a 5 minute exposure)... so what will it do fleshy root tips??? Maybe it is not a problem but I am not sure I am willing to take that risk on my nicer collected trees???

The primary chemical in Orthene Fire Ant killer is Acephate which is used quite a bit for aphid control.

From a personal standpoint, I am not going to use orthene powder or a drench because of its hazardous nature to both me and my resident pets. That being said, I have further investigated and still cant find any scientific data (published) on the sensitivity of conifer roots to water temperatures of 115 to 120 F -- I also asked a local nursery senior scientist and bonsai practitioner if he had any experience with this subject -- he indicated he had no information on the impacts of conifer root soak at these temperatures for 5 - 10 minutes, but did indicate that the literature does indicate that black nursery containers in full sun can exceed temperatures of 140 F in the interior of the pot -- but it should be noted that this is indeed is air temperature.

Now as far as temperature is concerned , the hot water from my house water heater is 117 F coming out of the tap -- which means that I routinely showers for excess of 5 minutes in this temperature water without any scalding or other issues. -- Same thing with using the bathtub (for me not the tree!!) -- no issues have arisen here. So, in a couple of weeks I will try the hot water bath and see what happens with the root aphids. Per the local expert who initially provided the information, the tree will then winter over normally and be re-potted in the spring.