Evaluating Dryocosmus Kuriphilus-induced Damage on Castanea Sativa

This method was developed by relating leaf area loss due to the gall wasp attack to the main branch feature such as dormant buds, galls, and dead shoots involved. Considering and combining these feature in a composite damage index allow a realistic evaluation of the tree state during the entire epidemic process, including the recovery phase. The main advantage is that it reveals the real branch alteration even during the recovery phase when the presence of galls becomes poor.

We first had the idea for this method when we realized that Dryocosmus kuriphilus attack also causes corruption of the branch architecture beside gall-related reduction in leaf area. Though this method is species specific, the methodology used to create it can be adapted and implemented to any other tree species and related pest. In order to collect the data, arrange for a clipboard, a camping chair, secateurs, a telescopic tree pruner, and a 30-meter measuring tape.

Get tree climbing equipment for analysis if the top crown is above eight meters. While collecting, gather three types of branches which represent damaged, healthiest, and an intermediate one to constitute the entire branch diversity. Then, attach the start of the measuring tape near the blade of the telescopic tree pruner.

Then use the telescopic pruner to cut the branch. Once the branch is cut, record its cutting height, aspect, and whether the branch type is architectural or reiteration. Next, to gather general information about the branch, assign a unique ID and record the age and the maximum length of the branch from the first branching point to the apex.

First look for a sprout, which is a freshly formed structure that has grown during the current vegetative season from a developed bud on a shoot. Next gather an alive shoot, which is a sprout that has developed from the previous vegetative season with respect to the sampling date, then a dead shoot which has died either due to D.kuriphilus attack or naturally. Then collect the reactivated dormant buds which are freshly formed sprouts that have grown during the present vegetative season from a dormant bud on a multi-layer branch part that is older than the shoot.

Finally look for a gall on the shoot which usually develops on the base or along the axis of a sprout. Then count and record all the live and dead shoots, reactivated dormant buds, and all the galls on the shoots respectively. To calculate the damage composite index, select the section corresponding to the dead shoot, then calculate the proportion of the dead shoot.

Next calculate the proportion of the reactivated dormant bud. After measuring the reactivated dormant bud population, calculate the number of galls on the shoots. Then measure the damage composite index considering the population of dead shoot, reactivated dormant bud, and the number of galls.

Next measure the damage severity on the basis of the damage composite index scale. This plot represents early stages of infestation comparing between the DCI and the two MAIDs within the branches. In the plot the Y-axis represents a standardized severity scale where both DCI and the two MAIDs are very low, thereby indicating minimum damage in the early stages.

This plot compares the DCI and the two MAIDs during the peak stages of the infestation. The DCI represents a very high damage level when compared to both the MAIDs showing intermediate damage. Interestingly, in the peak and the recovery stages, a heterogeneous branch pattern is observed based on the damage incurred on the basis of the corruption level of the branch.

In the case of high corruption level, MAIDs tend to underestimate the real damage because they are only based on the presence of galls. The next two plots represent the DCI and the MAIDs in the recovery and the recovered stages of the infestation. During the recovery stage, the plot shows smaller yet significant differences between the DCI and the two MAIDs.

However there isn't any difference between the indices in the recovered stage, with the DCI and the two MAIDs showing somewhat similar values. The damage composite index allows to evaluate the real damage caused by Dryocosmus kuriphilus on the branch architecture. Combining this procedure with other methods, like the Sanasilva crown transparency approach and the traditional method for assessing the infestation degree, ensure a thorough pest assessment.

Specifically use this procedure to evaluate the branch architecture damage. Use the traditional method for assessing the infestation degrees such as the proportion of attacked bark to evaluate the pest population and use the Sanasilva crown transparency index for a general crown assessment. After watching this video, you should have a good understanding of how to apply the damage composite index to properly evaluate the impact of Dryocosmus kuriphilus on the branch architecture of the chestnut tree.