Tortoise beetles on sweet potatoes

Tuesday, July 9, 2019

These fascinating beetles are a minor pest of sweet potatoes.  Early in the season, damage can look quite alarming, but rarely hits yield-limiting or economically damaging levels.  The Golden Tortoise Beetle (Charidotella bicolor) and the Mottled Tortoise Beetle (Deloyala guttata) will often come in on slips.  Areas that are protected from predators (i.e. under row cover) tend to show greater damage.  In Nova Scotia, there is typically only one generation per year and they do not overwinter.  Growers typically start noticing feeding damage in early July.  Not to get wildly dorky, but the adults look like if C3PO and R2D2 had a baby (Figure 1).  Adults are 5 – 7 mm in length and are metallic gold or orange, but can shift to a redder colour when disturbed.

Figure 1. Adult tortoise beetles.

You may also notice golden tortoise beetle larvae in your sweet potatoes (Figures 2, 3).  Larvae yellowish to reddish-brown and are broad and flat with spikes.  They have an anal fork and will use it to shovel old skin and fecal matter onto the spines on their back.  This creates a "poop shield", which, unsurprisingly, deters predation.

Figure 2. Tortoise beetle larvae with "poop shield".
Figure 3. Clearly an effective predation deterrent.
Both adults and larvae will feed on sweet potatoes and other members of the Convolvulaceae family, such as field bindweed and morning glory, causing irregular small- to medium-sized holes (Figure 4).  Tortoise beetles are a minor pest of sweet potatoes and chemical control is usually not warranted.  Sweet potatoes are a vigorous crop and will typically outgrow the damage (Figure 5).

Figure 4. Tortoise beetle damage, July 11, 2017.
Figure 5. Tortoise beetle damage in the same field on August 30th, 2017. 
Written in part by Cassidy Coombs, Perennia summer student.



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