Uptake Damage from 2,4-D from a handgun application

A call to a Butte/ Padre 7th leaf orchard in the Hilmar/Livingston area provided some interesting symptoms associated with uptake from herbicides. Five days after a flood irrigation, the grower noticed that a few trees on the end of five  rows were collapsing (Figure1). The damage was occurring across varieties affecting two out of three scaffolds. The soil texture was a sand common to the Hilmar/Livingston area.

Figure 1: Overview of tree collapse. Figure 2: Damaged tissue progressing from the tree roots into the trunk

A closer inspection of the tree showed a sunken area on the bark, but no gumming was present. Bark removal revealed a large red canker progressing up the tree from the soil (Figure 2). Removing the soil, the damaged plant tissue was visible on the roots, but stopped about five feet from the trunk (Figure 2). At that point, the roots beyond that point appeared healthy. Leaves of the tree were yellow, maintaining green veins - similar to a few different nutrient deficiencies. Creating a cross section, it became clear that something was trans-located up the tree through the xylem - as evident by the dis-colorization of the tissue (Figure 3 and 4). This suggested that the problem was not due to a disease, but rather something chemical. 

Figures 3 and 4: Bark removal and cross section of the almond tree affected by 2,4-D uptake through improper herbicide application.

Speaking with the grower, we went through a variety of orchard activities that may have caused the damage.  That led to discussions about fertilizers, herbicides, and any other cultural practices. Everything seemed to be reasonable, so the conversation turned towards orchard activities that occurred prior to the flood event. The grower admitted that an herbicide application of 2,4-D was made  36 hours prior to the irrigation. 2,4-D was applied at the full label concentration and was used to spot treat weeds by handgun through the orchard.  

In most situations, properly applied herbicides will stay within the area of application. When over-applications of products are made, the product can move and cause tree damage due to its concentration. Since these products are water soluble, their ability to move increases when an irrigation occurs shortly after product application. Using a handgun to apply any herbicide is very inaccurate in applying the proper dose. In many occasions, handgun applications lead to a 10 X rate or greater application within the treated area. This over-application of product can be dangerous to trees - as shown above. I doubt that this damage would have occurred if a 1X concentration would have been applied.