After using Imidacloprid 350 on my poinsettias in doses of 0.26 c.c./Lt., and Metil tiophanate in drench beginning the short days, we have had a constant and increasing yellow colouring on the total number of plants. If anyone can give me any advise on what to do, I will appreciate it. Thank you.

Natalia-

We have several questions for you.....

Did the onset of the leaf yellowing correspond with the timing of the chemical applications? How was the health of the plants at the time of the application? What were environmental conditions like in the greenhouse at the time (light, temperature)?

Is the yellowing showing on the new foliage, older foliage, or an overall yellowing?

How is root health? Do you have a recent media and tissue analysis?

Pictures of the plants including roots would really be helpful here. The yellowing may be the result of a chemical application but it could also be nutrient stress. Please get back to us with answers to our questions so we can try to determine the cause of the yellowing.

Thank you!

The yellowing of the leafs began 12 days after the application of imidacloprid.
Inside the greenhouse we have temperatures from 60,8F in the early morning to 89,6F (16 to 32C).
Light is normally in 6000 F.C. under black shade cloth.
The damage can be seen mostly in the younger leafs which have burnt borders.
The extract from the pot exhibits an E.C. of 0,60.
I have some pictures to share, but I don't find how to attach them. Please let me know who should I send them to in order for them to be posted. Thank you.

Natalia -

Thanks for your patience here. We always have a lot of questions when were trying to get to the bottom of a problem.

Regarding your EC level, do you mean 6.0 mmhos/cm? That is very high if that is the case and could be contributing to the leaf yellowing and marginal burn.

We normally don't consider Imidacloprid a chemical that would cause leaf yellowing as long as it's applied correctly. Were any other chemicals applied at the same time (growth regulators, spray adjuvants)? When we think of leaf yellowing from a chemical application we usually see the yellowing immediately following the application or within a couple of days. Twelve days after the application probably means that the yellowing was not caused by the chemical.

The leaf yellowing and marginal burn could also be an indication of some nutrient stress. Do you have a recent media and foliar analysis? If not, we would recommend sending in some samples to see where nutrient levels are in the soil and tissue.

You can email pictures to rsiemonsma@eckeranch.com. We will take a look at the pictures and post them for you. Thanks!