Blackberry harvest is almost fully completed in Arkansas with the last bit of primocane fruit coming off now. Focus for many growers has now shifted towards plant and field maintenance.
Disease management is still important in the time between harvest and dormancy as there are several diseases than can affect the yield potential of canes the following year. We are beginning to see many of these diseases take over plantings with the sustained heat and humidity we generally experience this time of year. Below we will discuss what diseases to keep an eye out for and what management tactics should be prioritized.
Cultural Control Tactics
1. Remove all harvested floricanes (second-year canes) and burn them outside of the planting. This will lower disease inoculum within plantings significantly.
2. Maximize efforts in weed management to help increase airflow between rows of blackberries. The base of first-year canes are generally hardened-off enough by August to not be injured by directed applications of paraquat.
3. Clean up field edges and hedgerows to maximize airflow into plantings and remove all nearby wild blackberries where possible.
4. Excess nitrogen should be avoided as it can lead to excessive foliage and overall decreased airflow around canes.
5. Overhead irrigation should be avoided if possible. Anthracnose infection is much more likely when canes and leaves stay wet for extended periods of time.
Diseases to be Concerned with Post-Harvest
Anthracnose, caused by the fungus Elisnoe veneta, is often the most serious disease in Arkansas that infects canes after harvest. Spores moved around during rain events can infect the stems of plants and lead to loss of yield and quality in the following year. Cane lesions can begin to depress and lead to cracks in the stem that lead to yield and quality loss.
Protectant fungicides like Captan will help to prevent this infection from occurring, and fungicides with some systemic activity such as Quilt Xcel (FRAC 11 +3) or Pristine (FRAC 11 + 7) should offer some curative benefits for present cane lesions.
Cane and Leaf Rust
A disease we observed last year in September was leaf and cane rust, which is caused by the fungus Kuehneola uredinis. This disease is often confused with orange rust, which has no means of control except removing the plant. Leaf and cane rust (Picture 2) can be suppressed by many fungicides and is something we should be scouting for and responding to as it can lead to severe defoliation and potentially impact next year’s yield. If leaf or cane rust is observed on primocanes after removal of second-year canes, apply Abound (FRAC 11) or Cabrio (FRAC 11) or Quilt Xcel (FRAC 11 +3) or Rally (FRAC 3) or Tilt (FRAC 3) or Pristine (FRAC 11 + 7).
Leaf Spot Diseases
Leaf spot diseases such as Cercospora, Psuedocercospora, or Septoria often begin to appear in the bottom of the canopy where leaves stay wet for extended periods (Picture 3). In late summer these diseases can begin to move up the plant and lead to a large level of defoliation if not managed. These diseases will often be cleaned up when combination fungicides such as Quilt Xcel or Pristine are used for Anthracnose or leaf and cane rust control. A fungicide application of Quilt Xcel (FRAC 11 +3) or Pristine (FRAC 11 + 7) or Cabrio (FRAC 11) or Abound (FRAC 11) or Tilt (FRAC 3) should be made if symptomology is widespread on the lower canopy and appears to be moving farther up the canopy.
Guidelines for Disease Management Post-Harvest
Maximizing cultural control will be key in preventing serious disease issues. Anything that can be done to increase airflow and decrease the amount of inoculum present should be prioritized. In addition to these cultural practices, regular fungicide applications should continue after harvest to lower the amount of inoculum present. Captan every 10-14 days (depending on rainfall) should be used as a baseline protectant program post-harvest. An addition of Quilt Xcel with captan should be considered to enhance prevention of Anthracnose issues and cleanup both leaf spot diseases and cane and leaf rust.