Our earliest planted milo is booting now where sugarcane aphids were found two weeks prior. Infestations have increased to treatable thresholds. This field is 5 miles south of where SCA were originally found and are 100% infested with aphids covering 30-50% of the plants. This level is very high.
In many fields, I only find aphids in 1 or 2 spots. This makes scouting difficult if we want to catch them early. One thing to look for is shiny or glossy appearance on the leaves (as seen above). This is honeydew which is the sugary-rich liquid excreted from aphids and soft b0died insects. Even in a low infested field, you will see a little bits of a glossy substance on the tip of a leaf. Once you see this, turn it over and inspect for aphids. This is where I have found most of our hits in the field.
Threshold – Several threshold levels are being used in the Delta region for 2015. One conservative threshold is 25% infested leaves with 50+ aphids per leaf at whorl from preboot stage through dough stage. In MS, the threshold at pre-boot and boot stages is 20% infested plants with large aphid colonies (100+) and localized areas of heavy honeydew present. From bloom through dough stage the threshold is 30% infested plants. I think either of these sets of thresholds will prevent serious yield losses and would suggest using whichever threshold is easiest for you to use. Once threshold is reach do not delay application because infestations can very quickly go from the threshold level to 100% infested plants and hundreds of aphids per leaf.
Insecticide – PYRETHROID INSECTICIDES ARE NOT EFFECTIVE and may flare infestations by killing all the aphid predators. Regardless of the insecticide, rapidly expanding populations are difficult to control. Foliar insecticide options for SCA are:
- Transform WG (Dow AgroSciences) – Transform WG is not fully registered yet, but Georgia, Alabama and several other states haves a section 18 emergency exception approved for 2015 until Nov. 20, 2015. In my insecticide trails last season, rates of 1.0 and 1.5 oz per acre were effective. Use the 1.5 oz rate if aphid populations are increasing rapidly. The label allows for 2 applications per season and not more than 3 oz per acre per crop and has a 14 day PHI.
- Sivanto (Bayer Crop Protection) – Sivanto has a full section 3 label and a supplemental 2ee label for lower rates on sorghum and other grain crops. The 2ee rates are 4 – 7 fl. oz per acre. Sivanto was very effective in my trials at rates of 3, 5, and 7 fl. oz. per acre, so the 4 fl. oz. rate should be effective. At the 4 oz rate it can be applied up to 7 times during the season but has a 21 day PHI.
- Chlopyrifos (Lorsban Advanced, Nufos, other) – Lorsban is labeled at 1 to 2 pints per acre. The 2 pint rate has a 60 day harvest interval and 1 pint a 30 day harvest interval. The 2 pint rate was 80-90% effective in my trial last year but could not be used after the boot stage due the 60 day PHI. The 1 pint rate was variable and only partly effective. DO NOT USE CHLORPYRIFOS ON SWEET SORGHUM.
- Dimethoate ( Dimethoate, Cygon) – Is labeled up to 1 pint per acre with a 28 day PHI. Most dimethoate products cannot be used after head emergence. Dimethoate was variable in my trials and not recommended without further testing.